Rolled electroactive polymers

ABSTRACT

The invention describes rolled electroactive polymer devices. The invention also describes employment of these devices in a wide array of applications and methods for their fabrication. A rolled electroactive polymer device converts between electrical and mechanical energy; and includes a rolled electroactive polymer and at least two electrodes to provide the mechanical/electrical energy conversion. Prestrain is typically applied to the polymer. In one embodiment, a rolled electroactive polymer device employs a mechanism, such as a spring, that provides a force to prestrain the polymer. Since prestrain improves mechanical/electrical energy conversion for many electroactive polymers, the mechanism thus improves performance of the rolled electroactive polymer device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation and claims priority under 35 U.S.C.§120 from co-pending U.S. patent application Ser. No. 10/793,401 filedMar. 3, 2004, which is incorporated by reference for all purposes.

U.S. application Ser. No. 10/793,401 claimed priority under 35 U.S.C. §119(e) from U.S. Provisional Patent Application No. 60/451,742, entitled“Electroactive Polymer Roll Transducer,” filed Mar. 3, 2003 which isincorporated by reference for all purposes; and is acontinuation-in-part and claims priority under 35 U.S.C. §120 from U.S.patent application Ser. No. 10/154,449, filed May 21, 2002 (now U.S.Pat. No. 6,891,317 issued May 10, 2005) which claimed priority under 35U.S.C. § 119(e) from co-pending U.S. Provisional Patent Application No.60/293,003 filed on May 22, 2001, each of which is incorporated hereinby reference for all purposes.

U.S. GOVERNMENT RIGHTS

This application was made in part with government support under contractnumber N00014-00-C-0252 awarded by the Office of Naval Research. Thegovernment has certain rights in the invention.

BACKGROUND OF THE INVENTION

The present invention relates generally to electroactive polymer devicesthat convert between electrical energy and mechanical energy. Moreparticularly, the present invention relates to rolled electroactivepolymer devices and methods of fabricating these devices.

In many applications, it is desirable to convert between electricalenergy and mechanical energy. Exemplary applications requiringconversion from electrical to mechanical energy include robotics, pumps,speakers, sensors, microfluidics, shoes, general automation, diskdrives, and prosthetic devices. These applications include one or moretransducers that convert electrical energy into mechanical work—on amacroscopic or microscopic level. Exemplary applications requiringconversion from mechanical to electrical energy include sensors andgenerators.

New high-performance polymers capable of converting electrical energy tomechanical energy, and vice versa, are now available for a wide range ofenergy conversion applications. One class of these polymers,electroactive elastomers, is gaining wider attention. Electroactiveelastomers may exhibit high energy density, stress, andelectromechanical coupling efficiency. The performance of these polymersis notably increased when the polymers are prestrained in area. Forexample, a 10-fold to 25-fold increase in area significantly improvesperformance of many electroactive elastomers.

Conventionally, bulky and static frames are used to apply and maintainprestrain for a single layer of electroactive polymer. The frames alsoallow coupling between the polymer and the external environment. Theseframes occupy significantly more space and weigh much more than a singlepolymer layer, and may compromise the energy density and compactadvantages that these new polymers provide.

Thus, improved techniques for implementing these high-performancepolymers would be desirable.

SUMMARY OF THE INVENTION

The present invention overcomes limitations in the prior art andprovides new rolled electroactive polymer devices. The present inventionalso includes employment of these devices in a wide array ofapplications and methods for their fabrication. A rolled electroactivepolymer device converts between electrical and mechanical energy; andincludes a rolled electroactive polymer and at least two electrodes toprovide the mechanical/electrical energy conversion. Prestrain may beapplied to the polymer. In one embodiment, a rolled electroactivepolymer device employs a mechanism, such as a spring, that provides aforce to strain the polymer. In one embodiment, the mechanism adds toany prestrain previously established in the polymer. In other cases, noprestrain is previously applied in the polymer and the mechanismestablishes prestrain in the polymer. Since prestrain improvesmechanical/electrical energy conversion for many electroactive polymers,the mechanism thus improves performance of the rolled electroactivepolymer device. In addition, the mechanism may provide other benefitssuch as a varying force response with deflection, which may be tuned tothe needs of an application.

The rolled electroactive polymer transducer may be employed for one ormore functions. When a suitable voltage is applied to electrodes inelectrical communication with a rolled electroactive polymer, thepolymer deflects (actuation). This deflection may be used to domechanical work. Whether or not the polymer deflects, electrical statesimposed on the polymer may be used to vary the stiffness or dampingprovided by the polymer, which has various mechanical uses. When apreviously charged electroactive polymer deflects, the electric field inthe material is changed. The change in electric field may be used toproduce electrical energy—for generation or sensing purposes. Thus, somefunctions of use for an electroactive polymer include actuation,variable stiffness or damping, generation or sensing.

Rolled electroactive polymer devices allow for compact electroactivepolymer device designs. The rolled devices provide a potentially highelectroactive polymer-to-structure weight ratio, and can be configuredto actuate in many ways including linear axial extension/contraction,bending, and multi-degree of freedom actuators that combine bothextension and bending. Rolled electroactive polymers of the presentinvention also provide a simple alternative for obtaining multilayerelectroactive polymer devices.

In one aspect, the present invention relates to a device for convertingbetween electrical and mechanical energy. The device comprises atransducer comprising at least two electrodes and a rolled electroactivepolymer in electrical communication with the at least two electrodes.The device also comprises a mechanism having a first element operablycoupled to a first portion of the polymer and a second element operablycoupled to a second portion of the polymer. The mechanism provides aforce that strains at least a portion of the polymer.

In another aspect, the present invention relates to a method forfabricating an electroactive polymer device. The method comprisesdisposing at least two electrodes on an electroactive polymer. Themethod also comprises rolling the electroactive polymer about a springto produce a rolled electroactive polymer. The method further comprisessecuring the rolled electroactive polymer to maintain its rolledconfiguration.

In yet another aspect, the present invention relates to a device forconverting between electrical and mechanical energy. The devicecomprises a transducer comprising at least two electrodes and a rolledelectroactive polymer in electrical communication with the at least twoelectrodes. The device also comprises a spring having a first springportion operably coupled to a first portion of the polymer and a secondspring portion operably coupled to a second portion of the polymer.

Another aspect of the present invention provides a device for convertingbetween electrical and mechanical energy. The device may be generallycharacterized as comprising: a polymer roll transducer comprising a) anelectroactive polymer including at least one active area and b) at leasttwo electrodes in electrical communication with the active area whereinat least a portion of the electroactive polymer is wrapped upon itselfto form a roll; at least one support member coupled to the polymer rolltransducer for providing at least one of i) a force that strains atleast a portion of the polymer, ii) a force for controlling bending inthe polymer roll transducer and iii) combinations thereof; and at leastone mechanical linkage coupled to the polymer roll transducer forallowing a force or a moment generated in a first portion of theelectroactive polymer to be communicated to a second portion of theelectroactive polymer.

Yet another aspect of the present invention provides a method forfabricating an electroactive polymer device. The method may be generallycharacterized as comprising: a) disposing at least two electrodes on anelectroactive polymer; b) rolling the electroactive polymer about atleast one of a support member, a mechanical linkage, an end cap, a baseor combinations thereof to produce an electroactive polymer roll; and c)securing the electroactive polymer roll to maintain its rolledconfiguration. In a particular embodiment, the electroactive polymerroll may be cut at one or more locations to limit a propagation of aforce or a moment from a first portion of the electroactive polymer rollto a second portion of the electroactive polymer roll.

These and other features and advantages of the present invention will bedescribed in the following description of the invention and associatedfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a top view of a transducer portion before andafter application of a voltage, respectively, in accordance with oneembodiment of the present invention.

FIGS. 2A-2D illustrate a rolled electroactive polymer device inaccordance with one embodiment of the present invention.

FIG. 2E illustrates an end piece for the rolled electroactive polymerdevice of FIG. 2A in accordance with one embodiment of the presentinvention.

FIG. 3A illustrates a monolithic transducer comprising a plurality ofactive areas on a single polymer in accordance with one embodiment ofthe present invention.

FIG. 3B illustrates a monolithic transducer comprising a plurality ofactive areas on a single polymer, before rolling, in accordance with oneembodiment of the present invention.

FIG. 3C illustrates a rolled transducer that produces two-dimensionaloutput in accordance with one environment of the present invention.

FIG. 3D illustrates the rolled transducer of FIG. 3C with actuation forone set of radially aligned active areas.

FIGS. 3E-G illustrate exemplary vertical cross-sectional views of anested electroactive polymer device in accordance with one embodiment ofthe present invention.

FIGS. 3H-J illustrate exemplary vertical cross-sectional views of anested electroactive polymer device in accordance with anotherembodiment of the present invention.

FIG. 3K illustrates a rolled electroactive polymer device that allows adesigner to vary the deflection vs. force profile of the device.

FIGS. 3L-3Z illustrate energy efficient rolled electroactive polymerdevices designed to provide precisely controlled angular movements.

FIG. 4 illustrates an electrical schematic of an open loop variablestiffness/damping system in accordance with one embodiment of thepresent invention.

FIG. 5A is block diagram of one or more active areas connected to powerconditioning electronics.

FIG. 5B is a circuit schematic of a device employing a rolledelectroactive polymer transducer for one embodiment of the presentinvention.

FIGS. 6A-6D describe the manufacture of a rolled electroactive polymerdevice in accordance with one embodiment of the present invention.

FIG. 6E illustrates a substantially rectangular electrode patterned onthe facing side of an electroactive polymer held by stretching frame inaccordance with one embodiment of the present invention.

FIG. 6F illustrates a multiple layer rolled construction that includes asecond layer of electroactive polymer disposed on top of the electrodepolymer of FIG. 6E.

FIGS. 6G and 6H illustrate differing prestrain in a multilayer stackcomprising four layers.

FIG. 7 is a schematic of a sensor employing a rolled electroactivepolymer transducer according to one embodiment of the present invention.

FIGS. 8A-8C illustrate the fabrication and implementation of amultilayer electroactive polymer device using rolling techniques inaccordance with one embodiment of the present invention.

FIGS. 8D and 8E illustrate side perspective views of the pushrodapplication from FIG. 8C before and after actuation, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described in detail with reference to a fewpreferred embodiments as illustrated in the accompanying drawings. Inthe following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art, that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process steps and/or structureshave not been described in detail in order to not unnecessarily obscurethe present invention.

Electroactive Polymers

Before describing structures, fabrication and applications of rolledelectroactive polymers of the present invention, the basic principles ofelectroactive polymer construction and operation will first beilluminated. The transformation between electrical and mechanical energyin devices of the present invention is based on energy conversion of oneor more active areas of an electroactive polymer. Electroactive polymersare capable of converting between mechanical energy and electricalenergy. In some cases, an electroactive polymer may change electricalproperties (for example, capacitance and resistance) with changingmechanical strain.

To help illustrate the performance of an electroactive polymer inconverting between electrical energy and mechanical energy, FIG. 1Aillustrates a top perspective view of a transducer portion 10 inaccordance with one embodiment of the present invention. The transducerportion 10 comprises a portion of an electroactive polymer 12 forconverting between electrical energy and mechanical energy. In oneembodiment, an electroactive polymer refers to a polymer that acts as aninsulating dielectric between two electrodes and may deflect uponapplication of a voltage difference between the two electrodes (a‘dielectric elastomer’). Top and bottom electrodes 14 and 16 areattached to the electroactive polymer 12 on its top and bottom surfaces,respectively, to provide a voltage difference across polymer 12, or toreceive electrical energy from the polymer 12. Polymer 12 may deflectwith a change in electric field provided by the top and bottomelectrodes 14 and 16. Deflection of the transducer portion 10 inresponse to a change in electric field provided by the electrodes 14 and16 is referred to as ‘actuation’. Actuation typically involves theconversion of electrical energy to mechanical energy. As polymer 12changes in size, the deflection may be used to produce mechanical work.

FIG. 1B illustrates a top perspective view of the transducer portion 10including deflection. In general, deflection refers to any displacement,expansion, contraction, torsion, linear or area strain, or any otherdeformation of a portion of the polymer 12. For actuation, a change inelectric field corresponding to the voltage difference applied to or bythe electrodes 14 and 16 produces mechanical pressure within polymer 12.In this case, the unlike electrical charges produced by electrodes 14and 16 attract each other and provide a compressive force betweenelectrodes 14 and 16 and an expansion force on polymer 12 in planardirections 18 and 20, causing polymer 12 to compress between electrodes14 and 16 and stretch in the planar directions 18 and 20.

Electrodes 14 and 16 are compliant and change shape with polymer 12. Theconfiguration of polymer 12 and electrodes 14 and 16 provides forincreasing polymer 12 response with deflection. More specifically, asthe transducer portion 10 deflects, compression of polymer 12 brings theopposite charges of electrodes 14 and 16 closer and the stretching ofpolymer 12 separates similar charges in each electrode. In oneembodiment, one of the electrodes 14 and 16 is ground. For actuation,the transducer portion 10 generally continues to deflect untilmechanical forces balance the electrostatic forces driving thedeflection. The mechanical forces include elastic restoring forces ofthe polymer 12 material, the compliance of electrodes 14 and 16, and anyexternal resistance provided by a device and/or load coupled to thetransducer portion 10, etc. The deflection of the transducer portion 10as a result of an applied voltage may also depend on a number of otherfactors such as the polymer 12 dielectric constant and the size ofpolymer 12.

Electroactive polymers in accordance with the present invention arecapable of deflection in any direction. After application of a voltagebetween the electrodes 14 and 16, the electroactive polymer 12 increasesin size in both planar directions 18 and 20. In some cases, theelectroactive polymer 12 is incompressible, e.g. has a substantiallyconstant volume under stress. In this case, the polymer 12 decreases inthickness as a result of the expansion in the planar directions 18 and20. It should be noted that the present invention is not limited toincompressible polymers and deflection of the polymer 12 may not conformto such a simple relationship.

Application of a relatively large voltage difference between electrodes14 and 16 on the transducer portion 10 shown in FIG. 1A will causetransducer portion 10 to change to a thinner, larger area shape as shownin FIG. 1B. In this manner, the transducer portion 10 convertselectrical energy to mechanical energy. The transducer portion 10 mayalso be used to convert mechanical energy to electrical energy.

For actuation, the transducer portion 10 generally continues to deflectuntil mechanical forces balance the electrostatic forces driving thedeflection. The mechanical forces include elastic restoring forces ofthe polymer 12 material, the compliance of electrodes 14 and 16, and anyexternal resistance provided by a device and/or load coupled to thetransducer portion 10, etc. The deflection of the transducer portion 10as a result of an applied voltage may also depend on a number of otherfactors such as the polymer 12 dielectric constant and the size ofpolymer 12.

In one embodiment, electroactive polymer 12 is pre-strained. Pre-strainof a polymer may be described, in one or more directions, as the changein dimension in a direction after pre-straining relative to thedimension in that direction before pre-straining. The pre-strain maycomprise elastic deformation of polymer 12 and be formed, for example,by stretching the polymer in tension and fixing one or more of the edgeswhile stretched. Alternatively, as will be described in greater detailbelow, a mechanism such as a spring may be coupled to different portionsof an electroactive polymer and provide a force that strains a portionof the polymer. For many polymers, pre-strain improves conversionbetween electrical and mechanical energy. The improved mechanicalresponse enables greater mechanical work for an electroactive polymer,e.g., larger deflections and actuation pressures. In one embodiment,prestrain improves the dielectric strength of the polymer. In anotherembodiment, the prestrain is elastic. After actuation, an elasticallypre-strained polymer could, in principle, be unfixed and return to itsoriginal state.

In one embodiment, pre-strain is applied uniformly over a portion ofpolymer 12 to produce an isotropic pre-strained polymer. By way ofexample, an acrylic elastomeric polymer may be stretched by 200 to 400percent in both planar directions. In another embodiment, pre-strain isapplied unequally in different directions for a portion of polymer 12 toproduce an anisotropic pre-strained polymer. In this case, polymer 12may deflect greater in one direction than another when actuated. Whilenot wishing to be bound by theory, it is believed that pre-straining apolymer in one direction may increase the stiffness of the polymer inthe pre-strain direction. Correspondingly, the polymer is relativelystiffer in the high pre-strain direction and more compliant in the lowpre-strain direction and, upon actuation, more deflection occurs in thelow pre-strain direction. In one embodiment, the deflection in direction18 of transducer portion 10 can be enhanced by exploiting largepre-strain in the perpendicular direction 20. For example, an acrylicelastomeric polymer used as the transducer portion 10 may be stretchedby 10 percent in direction 18 and by 500 percent in the perpendiculardirection 20. The quantity of pre-strain for a polymer may be based onthe polymer material and the desired performance of the polymer in anapplication. Pre-strain suitable for use with the present invention isfurther described in commonly owned, copending U.S. patent applicationSer. No. 09/619,848, which is incorporated by reference for allpurposes.

Generally, after the polymer is pre-strained, it may be fixed to one ormore objects or mechanisms. For a rigid object, the object is preferablysuitably stiff to maintain the level of pre-strain desired in thepolymer. A spring or other suitable mechanism that provides a force tostrain the polymer may add to any prestrain previously established inthe polymer before attachment to the spring or mechanisms, or may beresponsible for all the prestrain in the polymer. The polymer may befixed to the one or more objects or mechanisms according to anyconventional method known in the art such as a chemical adhesive, anadhesive layer or material, mechanical attachment, etc.

Transducers and pre-strained polymers of the present invention are notlimited to any particular rolled geometry or type of deflection. Forexample, the polymer and electrodes may be formed into any geometry orshape including tubes and multi-layer rolls, rolled polymers attachedbetween multiple rigid structures, rolled polymers attached across aframe of any geometry—including curved or complex geometries, across aframe having one or more joints, etc. Deflection of a transduceraccording to the present invention includes linear expansion andcompression in one or more directions, bending, axial deflection whenthe polymer is rolled, deflection out of a hole provided on an outercylindrical around the polymer, etc. Deflection of a transducer may beaffected by how the polymer is constrained by a frame or rigidstructures attached to the polymer.

Materials suitable for use as an electroactive polymer with the presentinvention may include any substantially insulating polymer or rubber (orcombination thereof) that deforms in response to an electrostatic forceor whose deformation results in a change in electric field. One suitablematerial is NuSil CF19-2186 as provided by NuSil Technology ofCarpenteria, Calif. Other exemplary materials suitable for use as apre-strained polymer include silicone elastomers, acrylic elastomerssuch as VHB 4910 acrylic elastomer as produced by 3M Corporation of St.Paul, Minn., polyurethanes, thermoplastic elastomers, copolymerscomprising PVDF, pressure-sensitive adhesives, fluoroelastomers,polymers comprising silicone and acrylic moieties, and the like.Polymers comprising silicone and acrylic moieties may include copolymerscomprising silicone and acrylic moieties, polymer blends comprising asilicone elastomer and an acrylic elastomer, for example. Combinationsof some of these materials may also be used as the electroactive polymerin transducers of this invention.

Materials used as an electroactive polymer may be selected based on oneor more material properties such as a high electrical breakdownstrength, a low modulus of elasticity—(for large or small deformations),a high dielectric constant, etc. In one embodiment, the polymer isselected such that is has an elastic modulus at most about 100 MPa. Inanother embodiment, the polymer is selected such that is has a maximumactuation pressure between about 0.05 MPa and about 10 MPa, andpreferably between about 0.3 MPa and about 3 MPa. In another embodiment,the polymer is selected such that is has a dielectric constant betweenabout 2 and about 20, and preferably between about 2.5 and about 12.

An electroactive polymer layer in transducers of the present inventionmay have a wide range of thicknesses. In one embodiment, polymerthickness may range between about 1 micrometer and 2 millimeters.Polymer thickness may be reduced by stretching the film in one or bothplanar directions. In many cases, electroactive polymers of the presentinvention may be fabricated and implemented as thin films. Thicknessessuitable for these thin films may be below 50 micrometers.

As electroactive polymers of the present invention may deflect at highstrains, electrodes attached to the polymers should also deflect withoutcompromising mechanical or electrical performance. Generally, electrodessuitable for use with the present invention may be of any shape andmaterial provided that they are able to supply a suitable voltage to, orreceive a suitable voltage from, an electroactive polymer. The voltagemay be either constant or varying over time. In one embodiment, theelectrodes adhere to a surface of the polymer. Electrodes adhering tothe polymer are preferably compliant and conform to the changing shapeof the polymer. Correspondingly, the present invention may includecompliant electrodes that conform to the shape of an electroactivepolymer to which they are attached. The electrodes may be only appliedto a portion of an electroactive polymer and define an active areaaccording to their geometry. Several examples of electrodes that onlycover a portion of an electroactive polymer will be described in furtherdetail below.

Various types of electrodes suitable for use with the present inventionare described in commonly owned, copending U.S. patent application Ser.No. 09/619,848, which was previously incorporated by reference above.Electrodes described therein and suitable for use with the presentinvention include structured electrodes comprising metal traces andcharge distribution layers, textured electrodes comprising varying outof plane dimensions, conductive greases such as carbon greases or silvergreases, colloidal suspensions, high aspect ratio conductive materialssuch as carbon fibrils and carbon nanotubes, and mixtures of ionicallyconductive materials.

Materials used for electrodes of the present invention may vary.Suitable materials used in an electrode may include graphite, carbonblack, colloidal suspensions, thin metals including silver and gold,silver filled and carbon filled gels and polymers, and ionically orelectronically conductive polymers. In a specific embodiment, anelectrode suitable for use with the present invention comprises 80percent carbon grease and 20 percent carbon black in a silicone rubberbinder such as Stockwell RTV60-CON as produced by Stockwell Rubber Co.Inc. of Philadelphia, Pa. The carbon grease is of the type such asNyoGel 756G as provided by Nye Lubricant Inc. of Fairhaven, Mass. Theconductive grease may also be mixed with an elastomer, such as siliconelastomer RTV 118 as produced by General Electric of Waterford, N.Y., toprovide a gel-like conductive grease.

It is understood that certain electrode materials may work well withparticular polymers and may not work as well for others. By way ofexample, carbon fibrils work well with acrylic elastomer polymers whilenot as well with silicone polymers. For most transducers, desirableproperties for the compliant electrode may include one or more of thefollowing: low modulus of elasticity, low mechanical damping, lowsurface resistivity, uniform resistivity, chemical and environmentalstability, chemical compatibility with the electroactive polymer, goodadherence to the electroactive polymer, and the ability to form smoothsurfaces. In some cases, a transducer of the present invention mayimplement two different types of electrodes, e.g. a different electrodetype for each active area or different electrode types on opposing sidesof a polymer.

2. Rolled Electroactive Polymer Devices

FIGS. 2A-2D show a rolled electroactive polymer device 20 in accordancewith one embodiment of the present invention. FIG. 2A illustrates a sideview of device 20. FIG. 2B illustrates an axial view of device 20 fromthe top end. FIG. 2C illustrates an axial view of device 20 takenthrough cross section A-A. FIG. 2D illustrates components of device 20before rolling. Device 20 comprises a rolled electroactive polymer 22,spring 24, end pieces 27 and 28, and various fabrication components usedto hold device 20 together.

As illustrated in FIG. 2C, electroactive polymer 22 is rolled. In oneembodiment, a rolled electroactive polymer refers to an electroactivepolymer with, or without electrodes, wrapped round and round onto itself(e.g., like a poster) or wrapped around another object (e.g., spring24). The polymer may be wound repeatedly and at the very least comprisesan outer layer portion of the polymer overlapping at least an innerlayer portion of the polymer.

In one embodiment, a rolled electroactive polymer refers to a spirallywound electroactive polymer wrapped around an object or center. As theterm is used herein, rolled is independent of how the polymer achievesits rolled configuration.

As illustrated by FIGS. 2C and 2D, electroactive polymer 22 is rolledaround the outside of spring 24. Spring 24 provides a force that strainsat least a portion of polymer 22. The top end 24 a of spring 24 isattached to rigid endpiece 27. Likewise, the bottom end 24 b of spring24 is attached to rigid endpiece 28. The top edge 22 a of polymer 22(FIG. 2D) is wound about endpiece 27 and attached thereto using asuitable adhesive. The bottom edge 22 b of polymer 22 is wound aboutendpiece 28 and attached thereto using an adhesive. Thus, the top end 24a of spring 24 is operably coupled to the top edge 22 a of polymer 22 inthat deflection of top end 24 a corresponds to deflection of the topedge 22 a of polymer 22. Likewise, the bottom end 24 b of spring 24 isoperably coupled to the bottom edge 22 b of polymer 22 and deflectionbottom end 24 b corresponds to deflection of the bottom edge 22 b ofpolymer 22. Polymer 22 and spring 24 are capable of deflection betweentheir respective bottom top portions.

As mentioned above, many electroactive polymers perform better whenprestrained. For example, some polymers exhibit a higher breakdownelectric field strength, electrically actuated strain, and energydensity when prestrained. Spring 24 of device 20 provides forces thatresult in both circumferential and axial prestrain onto polymer 22.

Spring 24 is a compression spring that provides an outward force inopposing axial directions (FIG. 2A) that axially stretches polymer 22and strains polymer 22 in an axial direction. Thus, spring 24 holdspolymer 22 in tension in axial direction 35. In one embodiment, polymer22 has an axial prestrain in direction 35 from about 50 to about 300percent. As will be described in further detail below for fabrication,device 20 may be fabricated by rolling a prestrained electroactivepolymer film around spring 24 while it the spring is compressed. Oncereleased, spring 24 holds the polymer 22 in tensile strain to achieveaxial prestrain.

Spring 24 also maintains circumferential prestrain on polymer 22. Theprestrain may be established in polymer 22 longitudinally in direction33 (FIG. 2D) before the polymer is rolled about spring 24. Techniques toestablish prestrain in this direction during fabrication will bedescribed in greater detail below. Fixing or securing the polymer afterrolling, along with the substantially constant outer dimensions forspring 24, maintains the circumferential prestrain about spring 24. Inone embodiment, polymer 22 has a circumferential prestrain from about100 to about 500 percent. In many cases, spring 24 provides forces thatresult in anisotropic prestrain on polymer 22.

End pieces 27 and 28 are attached to opposite ends of rolledelectroactive polymer 22 and spring 24. FIG. 2E illustrates a side viewof end piece 27 in accordance with one embodiment of the presentinvention. Endpiece 27 is a circular structure that comprises an outerflange 27 a, an interface portion 27 b, and an inner hole 27 c.Interface portion 27 b preferably has the same outer diameter as spring24. The edges of interface portion 27 b may also be rounded to preventpolymer damage. Inner hole 27 c is circular and passes through thecenter of endpiece 27, from the top end to the bottom outer end thatincludes outer flange 27 a. In a specific embodiment, endpiece 27comprises aluminum, magnesium or another machine metal. Inner hole 27 cis defined by a hole machined or similarly fabricated within endpiece27. In a specific embodiment, endpiece 27 comprises ½ inch end caps witha ⅜ inch inner hole 27 c.

In one embodiment, polymer 22 does not extend all the way to outerflange 27 a and a gap 29 is left between the outer portion edge ofpolymer 22 and the inside surface of outer flange 27 a. As will bedescribed in further detail below, an adhesive or glue may be added tothe rolled electroactive polymer device to maintain its rolledconfiguration. Gap 29 provides a dedicated space on endpiece 27 for anadhesive or glue than the buildup to the outer diameter of the rolleddevice and fix to all polymer layers in the roll to endpiece 27. In aspecific embodiment, gap 29 is between about 0 mm and about 5 mm.

The portions of electroactive polymer 22 and spring 24 between endpieces 27 and 28 may be considered active to their functional purposes.Thus, end pieces 27 and 28 define an active region 32 of device 20 (FIG.2A). End pieces 27 and 28 provide a common structure for attachment withspring 24 and with polymer 22. In addition, each end piece 27 and 28permits external mechanical and detachable coupling to device 20. Forexample, device 20 may be employed in a robotic application whereendpiece 27 is attached to an upstream link in a robot and endpiece 28is attached to a downstream link in the robot. Actuation ofelectroactive polymer 22 then moves the downstream link relative to theupstream link as determined by the degree of freedom between the twolinks (e.g., rotation of link 2 about a pin joint on link 1).

In a specific embodiment, inner hole 27 c comprises an internal threadcapable of threaded interface with a threaded member, such as a screw orthreaded bolt. The internal thread permits detachable mechanicalattachment to one end of device 20. For example, a screw may be threadedinto the internal thread within end piece 27 for external attachment toa robotic element. For detachable mechanical attachment internal todevice 20, a nut or bolt to be threaded into each end piece 27 and 28and pass through the axial core of spring 24, thereby fixing the two endpieces 27 and 28 to each other. This allows device 20 to be held in anystate of deflection, such as a fully compressed state useful duringrolling. This may also be useful during storage of device 20 so thatpolymer 22 is not strained in storage.

In one embodiment, a stiff member or linear guide 30 is disposed withinthe spring core of spring 24. Since the polymer 22 in spring 24 issubstantially compliant between end pieces 27 and 28, device 20 allowsfor both axial deflection along direction 35 and bending of polymer 22and spring 24 away from its linear axis (the axis passing through thecenter of spring 24). In some embodiments, only axial deflection isdesired. Linear guide 30 prevents bending of device 20 between endpieces 27 and 28 about the linear axis. Preferably, linear guide 30 doesnot interfere with the axial deflection of device 20. For example,linear guide 30 preferably does not introduce frictional resistancebetween itself and any portion of spring 24. With linear guide 30, orany other suitable constraint that prevents motion outside of axialdirection 35, device 20 may act as a linear actuator or generator withoutput strictly in direction 35. Linear guide 30 may be comprised of anysuitably stiff material such as wood, plastic, metal, etc.

Polymer 22 is wound repeatedly about spring 22. For single electroactivepolymer layer construction, a rolled electroactive polymer of thepresent invention may comprise between about 2 and about 200 layers. Inthis case, a layer refers to the number of polymer films or sheetsencountered in a radial cross-section of a rolled polymer. In somecases, a rolled polymer comprises between about 5 and about 100 layers.In a specific embodiment, a rolled electroactive polymer comprisesbetween about 15 and about 50 layers.

In another embodiment, a rolled electroactive polymer employs amultilayer structure. The multilayer structure comprises multiplepolymer layers disposed on each other before rolling or winding. Forexample, a second electroactive polymer layer, without electrodespatterned thereon, may be disposed on an electroactive polymer havingelectrodes patterned on both sides. The electrode immediately betweenthe two polymers services both polymer surfaces in immediate contact.After rolling, the electrode on the bottom side of the electrodedpolymer then contacts the top side of the non-electroded polymer. Inthis manner, the second electroactive polymer with no electrodespatterned thereon uses the two electrodes on the first electrodedpolymer.

Other multilayer constructions are possible. For example, a multilayerconstruction may comprise any even number of polymer layers in which theodd number polymer layers are electroded and the even number polymerlayers are not. The upper surface of the top non-electroded polymer thenrelies on the electrode on the bottom of the stack after rolling.Multilayer constructions having 2, 4, 6, 8, etc., are possible thistechnique. In some cases, the number of layers used in a multilayerconstruction may be limited by the dimensions of the roll and thicknessof polymer layers. As the roll radius decreases, the number ofpermissible layers typically decrease is well. Regardless of the numberof layers used, the rolled transducer is configured such that a givenpolarity electrode does not touch an electrode of opposite polarity. Inone embodiment, multiple layers are each individually electroded andevery other polymer layer is flipped before rolling such that electrodesin contact each other after rolling are of a similar voltage orpolarity.

The multilayer polymer stack may also comprise more than one type ofpolymer For example, one or more layers of a second polymer may be usedto modify the elasticity or stiffness of the rolled electroactivepolymer layers. This polymer may or may not be active in thecharging/discharging during the actuation. When a non-active polymerlayer is employed, the number of polymer layers may be odd. The secondpolymer may also be another type of electroactive polymer that variesthe performance of the rolled product.

In one embodiment, the outermost layer of a rolled electroactive polymerdoes not comprise an electrode disposed thereon. This may be done toprovide a layer of mechanical protection, or to electrically isolateelectrodes on the next inner layer.

Device 20 provides a compact electroactive polymer device structure andimproves overall electroactive polymer device performance overconventional electroactive polymer devices. For example, the multilayerstructure of device 20 modulates the overall spring constant of thedevice relative to each of the individual polymer layers. In addition,the increased stiffness of the device achieved via spring 24 increasesthe stiffness of device 20 and allows for faster response in actuation,if desired.

In a specific embodiment, spring 24 is a compression spring such ascatalog number 11422 as provided by Century Spring of Los Angeles,Calif. This spring is characterized by a spring force of 0.91 lb/inchand dimensions of 4.38 inch free length, 1.17 inch solid length, 0.360inch outside diameter, 0.3 inch inside diameter. In this case, rolledelectroactive polymer device 20 has a height 36 from about 5 to about 7cm, a diameter 37 of about 0.8 to about 1.2 cm, and an active regionbetween end pieces of about 4 to about 5 cm. The polymer ischaracterized by a circumferential prestrain from about 300 to about 500percent and axial prestrain (including force contributions by spring 24)from about 150 to about 250 percent.

Device 20 has many functional uses. As will be described in furtherdetail below, electroactive polymers of the present invention may beused for actuation, generation, sensing, variable stiffness and damping,or combinations thereof. Thus, device 20 may be used in roboticapplication for actuation and production of mechanical energy.Alternatively, rolled device 20 may contribute to stiffness and dampingcontrol of a robotic link. Thus, either end piece 27 or 28 may becoupled to a potentially moving mechanical link to receive mechanicalenergy from the link and damp the motion. In this case, polymer 22converts this mechanical energy to electrical energy according totechniques described below.

Although device 20 is illustrated with a single spring 24 disposedinternal to the rolled polymer, it is understood that additionalstructures such as another spring external to the polymer may also beused to provide strain and prestrain forces. These external structuresmay be attached to device 20 using end pieces 27 and 28 for example.

The present invention also encompasses mechanisms, other than a spring,used in a rolled electraoctive polymer device to apply a force thatstrains a rolled polymer. As the term is used herein, a mechanism usedto provide strain onto a rolled electroactive polymer generally refersto a system or an arrangement of elements that are capable of providinga force to different portions of a rolled electroactive polymer. In manycases, the mechanism is flexible (e.g., a spring) or has moving parts(e.g., a pneumatic cylinder). The mechanism may also comprises rigidparts (see the frame of FIG. 8B). Strain may also be achieved usingmechanisms such as hydraulic actuators, pneumatic actuators, andmagnetic systems (e.g., FIG. 3K), for example. Alternatively,compressible materials and foams may be disposed internal to the roll toprovide the strain forces and allow for axial deflection.

Generally, the mechanism provides a force that onto the polymer. In oneembodiment, the force changes the force vs. deflection characteristicsof the device, such as to provide a negative force response, asdescribed below. In another embodiment, the force strains the polymer.This latter case implies that the polymer deflects in response to theforce, relative to its deflection state without the effects of themechanism. This strain may include prestrain as described above. In oneembodiment, the mechanism maintains or adds to any prestrain previouslyestablished in the polymer, such prestrain provided by a fixture duringrolling as described below. In another embodiment, no prestrain ispreviously applied in the polymer and the mechanism establishesprestrain in the polymer.

In one embodiment, the mechanism is another elastomer that is similar ordifferent from the electroactive polymer. For example, this secondelastomer may be disposed as a nearly-solid rubber core that is axiallycompressed before rolling (to provide an axial tensile prestrain on theelectroactive polymer). The elastomer core can have a thin hole for arigid rod to facilitate the rolling process. If lubricated, the rigidrod may be slid out from the roll after fabrication. One may also make asolid elastomer roll tightly wound with electroactive polymer using asimilar technique.

The mechanism and its constituent elements are typically operablycoupled to the polymer such that the strain is achieved. This mayinclude fixed or detachable coupling, permanent attachment, etc. In thecase of the spring above, operable coupling includes the use of anadhesive, such as glue, that attaches opposite ends of the spring toopposite ends of the polymer. An adhesive is also used to attach therolled polymer to the frame in FIG. 8B. The coupling may be direct orindirect, e.g., the magnet 252 of FIG. 3K is attached to the end piece242, which is attached to the rolled polymer. One of skill in the art isaware of numerous techniques to couple or attach two mechanicalstructures together, and these techniques are not expansively discussedherein for sake of brevity.

Rolled electroactive polymers of the present invention have numerousadvantages. Firstly, these designs provide a multilayer device withouthaving to individually frame each layer; and stack numerous frames (seeFIG. 8B). In addition, the cylindrical package provided by these devicesis advantageous to some applications where long and cylindricalpackaging is advantageous over flat packaging associated with planarelectroactive polymer devices. In addition, using a larger number ofpolymer layers in a roll improves reliability of the device and reducessensitivity to imperfections and local cracks in any individual polymerlayer.

Alternate Rolled Electroactive Polymer Device Designs

Multiple Active Areas

In some cases, electrodes cover a limited portion of an electroactivepolymer relative to the total area of the polymer. This may be done toprevent electrical breakdown around the edge of a polymer, to allow forpolymer portions to facilitate a rolled construction (e.g., an outsidepolymer barrier layer), to provide multifunctionality, or to achievecustomized deflections for one or more portions of the polymer. As theterm is used herein, an active area is defined as a portion of atransducer comprising a portion of an electroactive polymer and one ormore electrodes that provide or receive electrical energy to or from theportion. The active area may be used for any of the functions describedbelow. For actuation, the active area includes a portion of polymerhaving sufficient electrostatic force to enable deflection of theportion. For generation or sensing, the active area includes a portionof polymer having sufficient deflection to enable a change inelectrostatic energy. A polymer of the present invention may havemultiple active areas.

In accordance with the present invention, the term “monolithic” is usedherein to refer to electroactive polymers and transducers comprising aplurality of active areas on a single polymer. FIG. 3A illustrates amonolithic transducer 150 comprising a plurality of active areas on asingle polymer 151 in accordance with one embodiment of the presentinvention. The monolithic transducer 150 converts between electricalenergy and mechanical energy. The monolithic transducer 150 comprises anelectroactive polymer 151 having two active areas 152 a and 152 b.Polymer 151 may be held in place using, for example, a rigid frame (notshown) attached at the edges of the polymer. Coupled to active areas 152a and 152 b are wires 153 that allow electrical communication betweenactive areas 152 a and 152 b and allow electrical communication withcommunication electronics 155.

Active area 152 a has top and bottom electrodes 154 a and 154 b that areattached to polymer 151 on its top and bottom surfaces 151 c and 151 d,respectively. Electrodes 154 a and 154 b provide or receive electricalenergy across a portion 151 a of the polymer 151. Portion 151 a maydeflect with a change in electric field provided by the electrodes 154 aand 154 b. For actuation, portion 151 a comprises the polymer 151between the electrodes 154 a and 154 b and any other portions of thepolymer 151 having sufficient electrostatic force to enable deflectionupon application of voltages using the electrodes 154 a and 154 b. Whenactive area 152 a is used as a generator to convert from electricalenergy to mechanical energy, deflection of the portion 151 a causes achange in electric field in the portion 151 a that is received as achange in voltage difference by the electrodes 154 a and 154 b.

Active area 152 b has top and bottom electrodes 156 a and 156 b that areattached to the polymer 151 on its top and bottom surfaces 151 c and 151d, respectively. Electrodes 156 a and 156 b provide or receiveelectrical energy across a portion 151 b of the polymer 151. Portion 151b may deflect with a change in electric field provided by the electrodes156 a and 156 b. For actuation, portion 151 b comprises the polymer 151between the electrodes 156 a and 156 b and any other portions of thepolymer 151 having sufficient stress induced by the electrostatic forceto enable deflection upon application of voltages using the electrodes156 a and 156 b. When active area 152 b is used as a generator toconvert from electrical energy to mechanical energy, deflection of theportion 151 b causes a change in electric field in the portion 151 bthat is received as a change in voltage difference by the electrodes 156a and 156 b.

Active areas for an electroactive polymer may be easily patterned andconfigured using conventional electroactive polymer electrodefabrication techniques. Multiple active area polymers and transducersare further described in 09/779,203 now U.S. Pat. No. 6,664,718, each ofwhich is incorporated herein by reference for all purposes. Given theability to pattern and independently control multiple active areasallows rolled transducers of the present invention to be employed inmany new applications; as well as employed in existing applications innew ways.

FIG. 3B illustrates a monolithic transducer 170 comprising a pluralityof active areas on a single polymer 172, before rolling, in accordancewith one embodiment of the present invention. Transducer 170 comprisesindividual electrodes 174 on the facing polymer side 177. The oppositeside of polymer 172 (not shown) may include individual electrodes thatcorrespond in location to electrodes 174, or may include a commonelectrode that spans in area and services multiple or all electrodes 174and simplifies electrical communication. Active areas 176 then compriseportions of polymer 172 between each individual electrode 174 and theelectrode on the opposite side of polymer 172, as determined by the modeof operation of the active area. For actuation for example, active area176 a for electrode 174 a includes a portion of polymer 172 havingsufficient electrostatic force to enable deflection of the portion, asdescribed above.

Active areas 176 on transducer 170 may be configured for one or morefunctions. In one embodiment, all active areas 176 are all configuredfor actuation. In another embodiment suitable for use with roboticapplications, one or two active areas 176 are configured for sensingwhile the remaining active areas 176 are configured for actuation. Inthis manner, a rolled electroactive polymer device using transducer 170is capable of both actuation and sensing. Any active areas designatedfor sensing may each include dedicated wiring to sensing electronics, asdescribed below.

At shown, electrodes 174 a-d each include a wire 175 a-d attachedthereto that provides dedicated external electrical communication andpermits individual control for each active area 176 a-d. Electrodes 174e-i are all electrical communication with common electrode 177 and wire179 that provides common electrical communication with active areas 176e-i. Common electrode 177 simplifies electrical communication withmultiple active areas of a rolled electroactive polymer that areemployed to operate in a similar manner. In one embodiment, commonelectrode 177 comprises aluminum foil disposed on polymer 172 beforerolling. In one embodiment, common electrode 177 is a patternedelectrode of similar material to that used for electrodes 174 a-i, e.g.,carbon grease.

For example, a set of active areas may be employed for one or more ofactuation, generation, sensing, changing the stiffness and/or damping,or a combination thereof. Suitable electrical control also allows asingle active area to be used for more than one function. For example,active area 174 a may be used for actuation and variable stiffnesscontrol of a robotic limb in a robotics application. The same activearea may also be used for generation to produce electrical energy basedon motion of the robotic limb. Suitable electronics for each of thesefunctions are described in further detail below. Active area 174 b mayalso be flexibly used for actuation, generation, sensing, changingstiffness, or a combination thereof. Energy generated by one active areamay be provided to another active area, if desired by an application.Thus, rolled polymers and transducers of the present invention mayinclude active areas used as an actuator to convert from electrical tomechanical energy, a generator to convert from mechanical to electricalenergy, a sensor that detects a parameter, or a variable stiffnessand/or damping device that is used to control stiffness and/or damping,or combinations thereof.

In one embodiment, multiple active areas employed for actuation arewired in groups to provide graduated electrical control of force and/ordeflection output from a rolled electroactive polymer device. Forexample, a rolled electroactive polymer transducer many have 50 activeareas in which 20 active areas are coupled to one common electrode, 10active areas to a second common electrode, another 10 active areas to athird common electrode, 5 active areas to a fourth common electrode inthe remaining five individually wired. Suitable computer management andon-off control for each common electrode then allows graduated force anddeflection control for the rolled transducer using only binary on/offswitching. The biological analogy of this system is motor units found inmany mammalian muscular control systems. Obviously, any number of activeareas and common electrodes may be implemented in this manner to providea suitable mechanical output or graduated control system.

Multiple Degree of Freedom Rolled Devices

In another embodiment, multiple active areas on an electroactive polymerare disposed such subsets of the active areas radially align afterrolling. For example, the multiple the active areas may be disposed suchthat, after rolling, active areas are disposed every 90 degrees in theroll. These radially aligned electrodes may then be actuated in unity toallow multiple degree of freedom motion for a rolled electroactivepolymer device.

FIG. 3C illustrates a rolled transducer 180 capable of two-dimensionaloutput in accordance with one environment of the present invention.Transducer 180 comprises an electroactive polymer 182 rolled to provideten layers. Each layer comprises four radially aligned active areas. Thecenter of each active area is disposed at a 90 degree increment relativeto its neighbor. FIG. 3C shows the outermost layer of polymer 182 andradially aligned active areas 184, 186, and 188, which are disposed suchthat their centers mark 90 degree increments relative to each other. Afourth radially aligned active area (not shown) on the backside ofpolymer 182 has a center approximately situated 180 degrees fromradially aligned active area 186.

Radially aligned active area 184 may include common electricalcommunication with active areas on inner polymer layers having the sameradial alignment. Likewise, the other three radially aligned outeractive areas 182, 186, and the back active area not shown, may includecommon electrical communication with their inner layer counterparts. Inone embodiment, transducer 180 comprises four leads that provide commonactuation for each of the four radially aligned active area sets.

FIG. 3D illustrates transducer 180 with radially aligned active area188, and its corresponding radially aligned inner layer active areas,actuated. Actuation of active area 188, and corresponding inner layeractive areas, results in axial expansion of transducer 188 on theopposite side of polymer 182. The result is lateral bending oftransducer 180, approximately 180 degrees from the center point ofactive area 188. The effect may also be measured by the deflection of atop portion 189 of transducer 180, which traces a radial arc from theresting position shown in FIG. 3C to his position at shown in FIG. 3D.Varying the amount of electrical energy provided to active area 188, andcorresponding inner layer active areas, controls the deflection of thetop portion 189 along this arc. Thus, top portion 189 of transducer 180may have a deflection as shown in FIG. 3D, or greater, or a deflectionminimally away from the position shown in FIG. 3C. Similar bending in ananother direction may be achieved by actuating any one of the otherradially aligned active area sets.

Combining actuation of the radially aligned active area sets produces atwo-dimensional space for deflection of top portion 189. For example,radially aligned active area sets 186 and 184 may be actuatedsimultaneously to produce deflection for the top portion in a 45 degreeangle corresponding to the coordinate system shown in FIG. 3C.Decreasing the amount of electrical energy provided to radially alignedactive area set 186 and increasing the amount of electrical energyprovided to radially aligned active area set 184 moves top portion 189closer to the zero degree mark. Suitable electrical control then allowstop portion 189 to trace a path for any angle from 0 to 360 degrees, orfollow variable paths in this two dimensional space.

Transducer 180 is also capable of three-dimensional deflection.Simultaneous actuation of active areas on all four sides of transducer180 will move top portion 189 upward. In other words, transducer 180 isalso a linear actuator capable of axial deflection based on simultaneousactuation of active areas on all sides of transducer 180. Coupling thislinear actuation with the differential actuation of radially alignedactive areas and their resulting two-dimensional deflection as justdescribed above, results in a three dimensional deflection space for thetop portion of transducer 180. Thus, suitable electrical control allowstop portion 189 to move both up and down as well as tracetwo-dimensional paths along this linear axis.

Although transducer 180 is shown for simplicity with four radiallyaligned active area sets disposed at 90 degree increments, it isunderstood that transducers of the present invention capable of two- andthree-dimensional motion may comprise more complex or alternate designs.For example, eight radially aligned active area sets disposed at 45degree increments. Alternatively, three radially aligned active areasets disposed at 120 degree increments may be suitable for 2D and 3-Dmotion.

In addition, although transducer 180 is shown with only one set of axialactive areas, the structure of FIG. 3C is modular. In other words, thefour radially aligned active area sets disposed at 90 degree incrementsmay occur multiple times in an axial direction. For example, radiallyaligned active area sets that allow two- and three-dimensional motionmay be repeated ten times to provide a snake like robotic manipulatorwith ten independently controllable links.

Nested Rolled Electroactive Polymer Devices

Some applications desire an increased stroke from a rolled electroactivepolymer device. In one embodiment, a nested configuration is used toincrease the stroke of an electroactive polymer device. In a nestedconfiguration, one or more electroactive polymer rolls are placed in thehollow central part of another electroactive polymer roll.

FIGS. 3E-G illustrate exemplary cross-sectional views of a nestedelectroactive polymer device 200, taken through the vertical midpoint ofthe cylindrical roll, in accordance with one embodiment of the presentinvention. Nested device 200 comprises three electroactive polymer rolls202, 204, and 206. Each polymer roll 202, 204, and 206 includes a singleactive area that provides uniform deflection for each roll. Electrodesfor each polymer roll 202, 204, and 206 may be electrically coupled toactuate (or produce electrical energy) in unison, or may be separatelywired for independent control and performance. The bottom ofelectroactive polymer roll 202 is connected to the top of the next outerelectroactive polymer roll, namely roll 204, using a connector 205.Connector 205 transfers forces and deflection from one polymer roll toanother. Connector 205 preferably does not restrict motion between therolls and may comprise a low friction and insulating material, such asTeflon. Likewise, the bottom of electroactive polymer roll 204 isconnected to the top of the outermost electroactive polymer roll 206.The top of polymer roll 202 is connected to an output shaft 208 thatruns through the center of device 200. Although nested device 200 isshown with three concentric electroactive polymer rolls, it isunderstood that a nested device may comprise another number ofelectroactive polymer rolls.

Output shaft 208 may provide mechanical output for device 200 (ormechanical interface to external objects). Bearings may be disposed in abottom housing 212 and allow substantially frictionless linear motion ofshaft 208 axially through the center of device 200. Housing 212 is alsoattached to the bottom of roll 206 and includes bearings that allowtravel of shaft 208 through housing 212.

The deflection of shaft 208 comprises a cumulative deflection of eachelectroactive polymer roll included in nested device 200. Morespecifically, individual deflections of polymer roll 202, 204 and 206will sum to provide the total linear motion output of shaft 208. FIG. 3Eillustrates nested electroactive polymer device 200 with zerodeflection. In this case, each polymer roll 202, 204 and 206 is in anunactuated (rest) position and device 200 is completely contracted. FIG.3F illustrates nested electroactive polymer device 200 with 20% strainfor each polymer roll 202, 204 and 206. Thus, shaft 208 comprises a 60%overall strain relative to the individual length of each roll.Similarly, FIG. 3G illustrates nested electroactive polymer device 200with 50% strain for each polymer roll 202, 204 and 206. In this case,shaft 208 comprises a 150% overall strain relative to the individuallength of each roll. By nesting multiple electroactive polymer rollsinside each other, the strains of individual rolls add up and provide alarger net stroke than would be achieved using a single roll. Nestedelectroactive polymer rolled devices are then useful for applicationsrequiring large strains and compact packages.

In another embodiment, shaft 208 may be a shaft inside a tube, whichallows the roll to expand and contract axially without bending inanother direction. While it would be advantageous in some situations tohave 208 attached to the top of 202 and running through bearings, shaft208 could also be two separate pieces: 1) a shaft connected to 212 andprotruding axially about ⅘ of the way toward the top of 206, and 2) atube connected to the top of 206 and protruding axially about ⅘ of theway toward 212, partially enveloping the shaft connected to 212.

FIGS. 3H-J illustrate exemplary vertical cross-sectional views of anested electroactive polymer device 220 in accordance with anotherembodiment of the present invention. Nested device 220 comprises threeelectroactive polymer rolls 222, 224, and 226. Each polymer roll 222,224, and 226 includes a single active area that provides uniformdeflection for each roll.

In this configuration, adjacent electroactive polymer rolls areconnected at their common unconnected end. More specifically, the bottomof electroactive polymer roll 222 is connected to the bottom of the nextouter electroactive polymer roll, namely roll 224. Likewise, the top ofelectroactive polymer roll 224 is connected to the top of the outermostelectroactive polymer roll 226. The top of polymer roll 222 is connectedto an output shaft 228 that runs through the center of device 220.Similar to as that described with respect to shaft 208, shaft 222 may bea shaft inside a tube, which allows the roll to expand and contractaxially without bending in another direction.

FIG. 3H shows the unactuated (rest) position of device 220. FIG. 3Ishows a contracted position of device 220 via actuation of polymer roll224. FIG. 3J shows an extended position of device 220 via actuation ofpolymer rolls 222 and 226. In the unactuated (rest) position of FIG. 3H,the shaft 208 position will be somewhere between the contracted positionof FIG. 3I and the extended position of FIG. 3J, depending on the axiallengths of each individual roll.

This nested design may be repeated with an increasing number of layersto provide increased deflection. Actuating every other roll—tarting fromthe first nested roll—causes shaft 228 to contract. Actuating everyother roll—starting from the outermost roll—causes shaft 228 to extend.One benefit to the design of nested device 220 is that charge may beshunted from one polymer roll to another, thus conserving overall energyusage. It is worth noting that each device 200 or 220 may be operated asa high strain generator or sensor that receives mechanical energy viashaft 208 or 228, as will be described in further detail below.

Negative Spring Constant Designs

A mechanism of the present invention may vary the force it provides withdeflection of the transducer or device. For rolled electroactive polymerdevices that employ a spring, as the device axially extends, the outputforce of the device typically decreases as a result of the spring. Inmany applications, it is desirable to implement mechanical input, suchas a linear actuator, whose output force is constant over the range ofdeflection—or increases with extension—according to the needs of theapplication. Such constant or negative spring constant mechanical inputmay be achieved using several mechanisms. Indeed, many such mechanismscould be attached to a rolled actuator externally or within the hollowinterior. Additionally, it is also possible to make the spring structureitself operate as a constant or negative spring constant spring. Forexample, the spring could be made by stacking several Belleville washerson a rigid rod with a flange at one to restrain the most proximalBelleville washer. Belleville washers are circular disks with a centralhole that are slightly conical. When compressed with sufficient forcethey can be made to pass through the point at which they are completelyflat and become conical in the opposite direction from the originalconfiguration. This flange is attached to one end of the roll. At theother end of the stack is a flat washer that is attached to the otherend of the roll that restrains and allows the rolled polymer material tocompress the Belleville washers past the point at which they becomeunstable and exert a force to invert the orientation of the cone. Manyother negative spring constant mechanisms could be used that do notrequire Belleville washers. These mechanism need only be placed betweeneach washer in a stack of flat washers so that the entire stack behavesas a negative constant spring. In all these examples, the edges of thewashers provide support for the stretched polymer film. Other constantor negative spring constant mechanical input and there use to enhancethe output of dielectric elastomer actuators are further described inpatent Ser. No. 09/779,373, which is incorporated herein for allpurposes.

FIG. 3K illustrates a rolled electroactive polymer device 240 thatallows a designer to vary the deflection vs. force profile of thedevice. Device 240 comprises end pieces 242 and 244, rolledelectroactive polymer 246, spring 248, rod 250, magnet 252,ferromagnetic core 254, and a magnet apparatus 256.

End pieces 242 and 244, rolled electroactive polymer 246, and spring 248are similar in structure and function as that described above withrespect to FIG. 2A. Rod 250 is coupled to end pieces 244 and slideswithin end piece 244. In one embodiment, the rod 250 is a solid rod thatextends in length from bottom end piece 242 to top end piece 244, andscrews into end piece 244 using mating threads in rod 250 and end piece244. In one embodiment, the entire rod 250 is made of 2 pieces: 1) a rodwith different diameters along the length of the rod (according to theembodiment shown in FIG. 3K, it would have four different diameters),and screwed into end piece 244 and 2) a tapered ferromagnetic core witha cylindrical hole of the same diameter as the top of rod 250. Thus, rod250 is fixed to end piece 244, and slides relative to end piece 242 andmagnet apparatus 256 as the polymer expands and contracts. Ferromagneticcore 254 is disposed on rod 250 somewhere between end pieces 242 and244. Ferromagnetic core 254 is a metal (e.g., steel) or similar materialthat provides magnetic attraction and forces between itself and amagnetic field. Connected rigidly to top end piece 242 is magneticapparatus 246, which supports and aligns a ring shaped magnet 252.Magnet 252 is thereby disposed concentrically with rod 250 andferromagnetic core 254. Magnet 252 produces a magnetic field thatattracts core 254.

Magnet 252 has a taper on its inner edge 253; and core 254 has acorresponding taper on its outer edge 255. With changing polymer 246deflection and motion of rod 250, magnet 252 is drawn closer to core254—thus exerting a force on slide 250 that increases as magnet 252nears core 254. In one embodiment, magnet 252 is magnetized radially.

Thus, as rod 250 extends, the output force of slide 250 due to spring248 gets weaker, but the output force of rod 250 due to the internalmagnetic assembly gets stronger. Spring 248 and the internal magneticassembly may be designed or configured to attain a desired forcerelationship with deflection. For example, spring 248 and internalmagnetic assembly may be designed and configured such that the net forceof rod 250 increases with polymer 246 deflection.

Since the force of magnetic attraction between magnet 252 and core 254decreases with the square of rod 250 deflection, designing andimplementing a 1:1 correspondence between linear slide deflection andmagnetic attraction would result in a narrow operating range. However,with the tapered magnet design of device 240, as rod 250 encounterslarge deflections, the force of magnetic attraction changes onlyslightly, thereby resulting in a larger deflection operating range.

In another embodiment, magnet 252 has a vertical inner edge (a cylinderwith a straight hole through it) and core 254 also has a matchingcylindrical outer profile. In this case, there is a force from magnet252 pulling core 254 completely inside magnet 252. As magnet 252 nearscore 254, it similarly draws core 254 into the magnetic cylinder, thusresulting in a net force on rod 250. This second configuration allowssimpler manufacture.

In one embodiment, device 240 also comprises a hard stop 258 attached toend piece 242. Hard stop 258 places a physical limit on how close magnet252 can get to core 254, and prevents contact between magnet 252 andcore 254. Alternatively, a barrier layer may be disposed between magnet252 and core 254, such as a layer of plastic, cardboard, foam, etc., toprevent metal on magnet contact.

Actuator Designs for Precise Angular Control

Previous examples of rolled actuators designs with the potential forboth 1) bending and lengthening motions (e.g., FIG. 3D) or 2)lengthening motions with linear output (e.g., see FIGS. 3E-3K) have beendescribed. FIGS. 3L-3Z illustrate energy efficient rolled electroactivepolymer devices designed to provide precisely controlled angularmovements, angular output, and angular stiffness control. These designs,provided for illustrated purposes only, may comprise one or more supportmembers coupled to a rolled polymer actuator and mechanical linkagesthat allow for force transfers between different portions of the rolledpolymer actuator. The apparatus and methods described with respect toFIGS. 3L-3Z are not necessarily limited to the rolled polymer actuatordesigns described in these figures and may be applicable to other rolledpolymer actuator designs or non-rolled electroactive polymer actuatorpolymer designs. For example, FIG. 3V illustrates a number of methodsfor fastening a rolled polymer actuator to an end-cap, such as clamping.These fastening methods may be applied to other rolled and non-rolledelectroactive polymer actuator designs.

FIG. 3L illustrates an embodiment of a rolled electroactive polymeractuator 800 with an angular output. FIG. 3L shows a cross-section ofthe device 800 and FIG. 3M shows a top view. On one end, a polymer roll801, which may include a plurality of active areas, is fixed to acylindrical base 802. Through the center of the polymer roll 801, asupport member 803 with a circular cross section is coupled at thecenter of the base at a fixed 90 degree angle. In other embodiments, thesupport member 803 may be located off center of the base and may befixed at angles different than 90 degrees. Further, the angle betweenthe support member 803 and the base 802 does not necessarily have to befixed. For instance, a linkage between the support member 803 and thebase 802, such a linkage providing a pivot point, may allow the anglebetween them to vary.

The cross section of the support member 803 may be of any shape, such asround or square. The cross sectional shape of the support member may beconstant along its length or may vary along its length (see FIG. 3U).The support member may be solid or hollow, such as a solid rod or ahollow tube.

In one embodiment, the support member 803 may comprise a plurality ofextendable nested tubes, such as telescoping tubes. Thus, the supportmember may be lengthened or shortened by fixing the nested tubes at aparticular length. For instance, the nested tubes may be pinned at aparticular length. By changing the length of the nested tubes, aninitial strain on the polymer roll may be increased or decreased.

In manufacture, the polymer may be rolled around and then secured to thetelescoping tubes. Initially, the tubes may be at their minimum length.Then, the tubes may be stretched to the final length and fixed inposition to provide a tensile force on the polymer roll.

The support member 803 is attached to an end cap 806 with flange 805 anda cylindrical bore 804. The support member 803 also includes acylindrical bore 804. The support member 803 and the end cap 806 areshaped to allow a pin 808 to be inserted through the cylindrical bore804 to provide a coupling between the support member 803 and the end cap806 and to allow the end cap 806 to rotate about the pin 808.

The polymer roll 801 is secured to the end cap 806. In one embodiment,the polymer roll 801 is stretched so that it exerts a force that pullsthe end cap 806 towards the base. The stretching is an initial strain(or pre-strain) on the polymer roll. The initial strain or pre-strain isin reference to the rolled actuator device 800 in an unactuatedposition. In this embodiment, in the unactuated position, the top of theend cap 806 is parallel to the base 802. In other embodiments, in theunactuated position, the top of the cap 806 and the base 802 may benon-parallel relative to one another. For instance, a force tunablespring may be used to set an initial angle between the end cap 806 andthe base in the unactuated position. In another embodiment, the pivotpoint may be located off center from the axis through the center of thesupport member 803. Placing the pivot point off-center results in aninitial non-horizontal angle to balance the moments about the pivotpoint generated by the polymer roll 801, which is in tension.

In FIG. 3L, the cross section of the polymer roll 801 shows two activeareas 801 a and 801 b opposite one another that may be actuated. Aspreviously described in FIGS. 3A-3D, the polymer roll 801 may bemonolithic comprising a plurality of active areas. In operation, avoltage may be applied to the active area 801 b. When the voltage isapplied to area 801 b, the polymer in this area lengthens and the endcap 806 rotates around the pin 808 through an angle 807. The ability ofthe polymer designs to produce large strains allows the end cap 806 tobe rotated through a large range of angles. For instance, the top of theend cap may be rotated from a horizontal position relative to the base802 to a nearly perpendicular position relative to the base in eitherdirection.

A logic device and conditioning electronics (not shown) in communicationwith the polymer roll 801 and coupled to the device 800 may be used toposition the end cap 806 at various angles 807 by controlling thevoltages supplied to the active areas of the roll polymer 801. Further,when the end cap 806 is rotated from a first angle to a second angle,the logic device and the conditioning electronics may be used to controla rate of rotation of the end cap 806. The logic device may include amemory for storing a table that relates an angular position to operatingparameters for the polymer roll 801, such as voltages and strains forthe active areas. The logic device may use the table to position the endcap 806. The logic device may be operable to vary the position of theend cap 806 as a function of time.

The device 800 may include one or more sensors for measuring operatingparameters of the device. A position of the end cap, an angular velocityof the end cap, an acceleration of the end cap, voltages on one portionsof polymer roll 801 and strains on one or more portions of the polymerroll 801 are examples of operating parameters that may be directlymeasured or deduced from sensor measurements. In some embodiments, themeasurements may be used in a feedback control loop for the device. Inother embodiments, the device 800 may be designed as part of a sensorand the measurements may be used to generate a sensed output provided bythe device. Further, details of logic devices, conditioning electronics,sensors and using rolled polymers for sensing purposes are describedwith respect to FIGS. 4, 5A, 5B and 7.

When the active area 801 b is actuated and the end cap is rotatedthrough angle 807, a portion of the polymer roll 801 is lengthened and aportion of the polymer roll 801 is shortened. Since the polymer roll 801is in tension, the portion that is shortened provides a rotationalmoment about the pivot point that helps to rotate the end-cap throughangle 807. The rotational moment generated by the unactuated portions ofthe polymer, such as 801 a, decreases the energy needed to rotate theend cap 806. In one embodiment, during operation of the device 807, theangle 807 may be defined as a difference between an initial angularposition and a second angular position.

Controlled angular output, such as, described in the paragraph above,may be used in many applications. For instance, the device 800 may beused as part of a servo-mechanism that controls the actuation of a sideview mirror of an automobile. As another example, the device 800 may beused as part of a biomemetic robot.

The end cap 806 provides a mechanical linkage between portions of thepolymer. In this case, the end cap 806 acts as a lever through the pivotpoint 804. In the present invention, many different types andcombinations of mechanical linkages may be used to allow forces andmoments to be communicated from a first portion of the polymer roll 801to a second portion of the polymer roll 801. Some examples of mechanicallinkages are described with respect to FIGS. 3P-3U.

The shape of the end cap 806 where the rolled polymer is attached may bevaried from the round shape in FIG. 3M. For instance, the top of the endcap 806 and the base 802 where the polymer roll 801 is attached may beovular. The ovular shape may be used to extend a length of a moment armrelative to the pivot point 804. In another example, the top of the endcap 806 and the base 802 may be different shapes, such as ovular andcircular or circles of two different radii.

When a shape with a center, such as a circle or an oval, is used for theportion of the end cap 806 where the polymer roll is attached, thecenter of the shape does not necessarily have to be aligned with thecenter of the support member 803. When the center of shape of the endcap 806 is placed off center relative to the center axis of the supportmember 803, the moments about the pivot point can be varied. Inaddition, the present invention is not limited to ovular and circularshapes, which is provided for illustrative purposes only.

The material of the support member 803 may be selected to support theload exerted by the stretched polymer roll 801 as well as any loadsexperienced during operation of the device 800. Metals, plastics,ceramics and composites are examples of suitable materials. Duringoperation of the device 800, the support member 803 may be designed tobe rigid under some conditions and flexible under others. For instance,if the device is exposed to a sudden impulsive load, the support member803 may be designed to bend to absorb the load rather than break in ananalogous manner to a human bone. The material of the end cap 806 or anyof the mechanical linkages of the present invention may be the same ordifferent than the support members. Metals, plastics, ceramics andcomposites are examples of suitable materials.

As shown in FIGS. 3N and 3O, the top of the end cap 806 may be shaped orinclude appendages. For instance, FIG. 3N shows a hexagonal cap mountedon top of the round end cap shown in FIG. 3M. As another example, FIG.3O shows a square appendage on top of the end cap 806. In oneembodiment, the shaped end cap or the appendage may be used for matingdevice 800 with another device 800 or other components. In anotherexample, a passive element or appendage may be added on top of the endcap 806 to extend the range of motion of the device 800. Also, anadditional linkage external could be attached to the end of the roll toincrease the bending angle achieved using mechanical leverage.

Via the end cap 806 or another suitable component of the device 800, aforce or a moment may be output. In addition, the device 800 may receivea force or a moment that is generated outside of the device via the endcap 806 or another suitable component. For instance, the device 800could be a component in a joystick and could receive forces or momentsfrom a person using the joystick.

When the device receives an outside force or an outside moment, thedevice 800 may generate a force or a moment in response. For example, inresponse to receiving an outside force one or more active areas of thepolymer 801 may be actuated to “stiffen” the device to make it moredifficult to move or to slow down a rate of movement of the device. Inanother example, the device 800 may vibrate or move in some other mannerin response to the force. These types of responses may be used as partof a force feedback device, such as part of an input device used on agaming console.

In another example, the device 800 could be used as a sensor thatmeasures a change in a parameter due to an input of an outside force ormoment to the device. For instance, in the joystick application, thedevice may be arranged to measure strains on different portions of thepolymer 801 resulting from receiving an input force. The measuredstrains, which may be output by the device 800, may be used to determinea relative position of the device 800. In another example, the device800 b may be arranged to sense changes in its configuration to determinea magnitude of a force received as an input to the device. Otherparameters that may be measured using the device 800 as part of a sensorinclude but are not limited to a linear position, an angular position, alinear velocity, an angular velocity, a linear acceleration, an angularacceleration and combinations thereof.

Returning to FIGS. 3L, the end cap 806 is used as a single mechanicallinkage to provide a communication of forces and moments betweendifferent portions of the polymer roll 801. The end cap 806 is connectedto the support member using a pin mechanism, which allows rotation inone direction. The present invention is not limited to the singlemechanical linkage, a pin connection mechanism or rotation in onedirection. In FIGS. 3P-3U, embodiments of devices with a) multiplemechanical linkages of varying types, b) multiple rotational degrees offreedom, c) different types of mechanical linkage connection schemes aredescribed.

In FIGS. 3P and 3Q, a cross section of a device 810 with a plurality ofmechanical linkages, 806, 812 a, 812 b and 812 c, for transferringforces and moments between different portions of the polymer roll 801are described. The mechanical linkages, 806, 812 a, 812 b and 812 c areeach coupled to support member 803. The mechanical linkages are alsocoupled to the polymer roll 801. In one embodiment, a portion of eachmechanical linkage may be attached to the polymer roll using anadhesive. The attachment scheme may vary from linkage to linkage. Forexample, the polymer roll 801 may be clamped to the end cap 806 andpinned to mechanical linkages 812 a-c. A few examples of attachmentschemes are later described with respect to FIG. 3V.

The device 810 may operate in a manner similar to the device 800described with respect to FIG. 3L. When a voltage is applied to anactive portion 801 b of the polymer roll 801, the active portion 801 bmay lengthen and rotate the end cap 806 through the angle 807. Theadditional mechanical linkages, 812 a-c, contribute rotational momentsthat may allow the device 810 to actuate more efficiently. Further,during operation of the device, the mechanical linkages, 812 a-c, mayprovide shape stability to the polymer roll 801. For instance, themechanical linkages may prevent the polymer roll 801 from neckingbetween the end cap 806 and the base 802.

Many different shapes, connection schemes and arrangements of mechanicallinkages may be used with the present invention. Different shapes ofmechanical linkages are described with respect to FIG. 3Q, differentarrangements are described with respect to FIGS. 3R and 3S and differentconnection schemes are described with respect to FIG. 3T. Forillustrative purposes, in FIG. 3Q, a few examples of mechanical linkageshapes are shown as a top view of mechanical linkage 812 a.

Shape 814 a is a circular disc with a bar for connecting to supportmember 803. Shape 814 b is a circular disc with outer portions of thedisc removed and a bar for connecting to support member 803. The removalof the outer portion of the disc eliminates contact and hence linkagewith portions of the polymer 801 as compared to 814 a. Shape 814 c ismore ovular and compact version of shape 814 b.

Shape 814 d is the shape 814 c with a square appendage on one side. Themovement of the mechanical linkage 812 a generates a rotational moment817 around axis 816. The square appendage on 814 d may be used totransfer energy from the rotational moment 817 to another portion ofdevice 810. For instance, in one embodiment, the square appendage may becoupled to a torsional spring that is wound or unwound when the polymerroll 801 is actuated. In one embodiment, the torsional spring may beused to generate a restoring force that helps to return an actuatedportion of the polymer roll 801 to its unactuated position.

As described with respect to the end cap 806 in FIG. 3L, the shape ofthe mechanical linkages may be non-symmetric about axis 816. Further,the shapes of the mechanical linkages 812 a-c may differ from oneanother, the shape of the end cap 806 and the shape of the base 802.Further, the shape of the mechanical linkage may not be planar. Forinstance, in FIG. 3P in the unactuated position of device 810, a firstportion of the mechanical linkage 812 a may be parallel to the end cap806 and a second portion of the mechanical linkage 812 a may be at angleto the end cap 806.

In embodiments of the present invention, an alignment of the couplingsof the mechanical linkages to the support member 803 and a type ofcoupling may vary from linkage to linkage. For instance, in oneembodiment, the end cap 806 may be coupled to the support member 803using a ball and socket joint (not shown). Mechanical linkage 812 a mayuse shape 814 b (see FIG. 3Q) to connect to the support member 803, themechanical linkage 812 b may use shape 814 b rotated 90 degrees (seeFIG. 3R) to connect to support member 803 and mechanical linkage 812 cmay use the same shape and alignment as linkage 812 a (See FIG. 3R) toconnect to support member 803.

In this example, the device 810 may use two pairs of active regions onthe polymer roll 801 aligned perpendicularly to one another. The fouractive regions on the polymer roll 801 may be actuated to position theend cap 806 with an orientation designated by two angles 818 and 819 asshown in FIG. 3S. The mechanical linkages, 812 a/812 c vs. 812 b,generate rotational moments that act around axes that are perpendicularto one another. These rotational moments may be used to reduce theenergy required to actuate the end cap 806 through angles 818 and 819 asshown in FIG. 3S.

As described above with respect to FIGS. 3P-3S, the mechanical linkagesof the present invention are not limited to pin systems. In FIG. 3T, anumber of embodiments of mechanical linkage connection schemes are shownfor illustrative purposes only as the present invention is not limitedto these embodiments. A pin connection scheme 811 a was previouslydescribed. A notched connection scheme 811 b comprises a groove 822 incircular cross member 820. A mechanical linkage 821 with a circularinner diameter less than outer diameter of the support member allows formovement in multiple directions about the groove 822. The size and shapeof the groove 822 may limit the range of motion of the mechanicallinkage. For instance, the groove may not extend around the entirecircumference of the support member 803.

A spherical connection scheme 811 c comprises a spherical shaped portion824 of support member 823. The mechanical linkage 825 may be rotated inmultiple dimensions about the spherical portion 824. In one embodiment,the support member 823 may include a cylindrical rather than sphericalshaped portion to limit the range of motion of mechanical linkage 825. Apaired protuberance connection scheme 811 d comprises two protuberances827 around a circumference of support member 826. The two protuberancesconfine a mechanical linkage within the two protuberances to aparticular range of motion.

The present invention is not limited to a plurality of separatemechanical linkages. In particular embodiments, the mechanical linkagesmay be linked to one another is some manner. For example, in oneembodiment of the present invention, a spring 830 is a used as amechanical linkage. Since the coils of the spring are all linkedtogether, communication of forces between different portions of themechanical linkage is possible. Further, the coils may be used totransfer forces and moments from different portions of the polymer rollalong its length when the active areas 801 a and 801 b of the polymerroll are actuated. In addition, the spring also may provide shapestability to the roll along its length.

In another embodiment of the present invention, a solid material such asa foam sleeve may be placed around support member 803. The foam sleevemay be employed as a mechanical linkage to transfer forces and momentsfrom a first portion of the polymer roll to a second portion of thepolymer roll. Further, the foam leave may be used to provide shapestability for the polymer roll.

The mechanical linkages, such as spring 803, do not have to be locatedalong the entire length of the support member 803. In one embodiment ofthe present invention in FIG. 3U, a spring 830, used as a mechanicallinkage, spans only a portion of the length of support member 803. Toprovide additional shape stability for the polymer roll 801, the supportmember comprises a flange 831 flange of some kind of material (e.g.,foam, plastic, metal) located below the spring 830.

In the present invention, the polymer roll 801 may be attached to themechanical linkages using a variety of methods. A few of these examplesare described with respect to FIG. 3V. In FIG. 3V, the polymer roll 801is attached to an end cap using an adhesive, a pin, and a clamp. The endcaps can be shaped to have ridges and/or lips for additional holdingforce. The clamp goes over the top of the end cap like a bottle cap. Acombination of attachment schemes may be used to attach the polymer rollto the mechanical linkage. For example, the polymer roll may be clampedand glued to the mechanical linkage. Further, the attachment schemes mayvary from mechanical linkage to mechanical linkage in the same device.For instance, the polymer roll 801 may be pinned and glued to a firstmechanical linkage and only glued to a second mechanical linkage in thesame device. In general, many types of fasteners may be used with thepresent invention and the invention is not limited to the examplesprovided above. Further, these attachment methods apply to all rollembodiments of the present invention and not only the examples describedwith respect to section 3.5.

In one embodiment, pins may be used to secure the polymer to a supportmember or mechanical linkage and in addition may be used as part of anelectrical connection scheme. Thus, the pins may be manufactured from anelectrically conductive material (In other embodiments of the presentinvention, the pins may be insulated.) When inserted through theelectroactive polymer, the pins may electrically connect the activeareas on multiple layers of the wrapped electroactive polymers. Further,the pins may connect two or more active areas on different portions ofthe polymer roll. For example, a pin may extend through one side of theroll, through the center of the roll and out the other side andelectrically connect side active areas on the opposite side of therolls.

In FIGS. 3L and 3P, an angular motion is provided at the end of device800 and device 810 through the end cap 806. The present invention is notso limited. Devices of the present invention may comprise a supportstructure within the polymer roll with one or more joints where angularrotation is possible. The one or more joints where angular rotation ispossible may be located at any position along the length of the polymerroll.

FIG. 3W shows a center cross-section of a device 870. The device 870includes an electroactive polymer roll with at least two active areas801 a and 801 b. Within the center of the polymer roll are two supportmembers, 840 and 841. The support members are coupled via pinned joint842. The pinned joint 842 is designed to allow the two support members,840 and 841, to rotate relative to one another. In device 870, thepolymer roll may be stretched and attached to the end caps of each ofthe support members 840 and 841. The stretching places an initial strain(pre-strain) on the polymer roll.

In one embodiment, the pinned joint 842 may be stopped to limit theamount of rotation. For example, the joint 842 may be stopped to allowthe support members to align vertically and for support member 840 torotate only to the right from the vertically aligned position. The joint842 may be stopped to allow a variety of angular ranges and is notlimited to being stopped with the support members in vertically alignedposition.

When active area 801 b is actuated, the polymer in the active arealengthens and support members 840 and 841 rotate toward one another suchthat the angle 843 between the support members is less than 180 degrees.Since the polymer roll is in tension, the unactuated portion of thepolymer 801 b may generate a rotational moment that helps to rotate thedevice 870 during actuation of the active area 801 a. This design mayhelp to minimize the energy needed to operate device 870. When theactive area 801 a is unactuated, the polymer in active area 801 ashortens and the device 870 is pulled back to an approximatelyvertically aligned position.

Many of the embodiments of the present invention have robotics relatedapplications. When designing actuators for robotics, a designer oftenlooks to nature for inspiration. For instance, humans and other animalsuse antagonistic muscle pairs. When one muscle of the antagonistic pairlengthens, the other muscle in the pair shortens. In FIGS. 3L, 3P, 3Q,when the devices, 800, 810 and 870, are operated, a first portion of theelectroactive polymer roll lengthens and a second portion of the polymerroll, linked to the first portion via a mechanical linkage, shortens.Thus, the configuration and operation of these devices can be said tomimic an antagonistic muscle pair found in humans in other animals.

Besides antagonistic muscle pairs, at joint interfaces (e.g., at theknee), the human muscular-skeletal system employs attachments for largeand small muscles. The attachments may be connected to antagonisticmuscle pairs. These attachments may overlap and produce different forcesand moments that aid in movement, balance and stability. In FIGS. 3X-Z,a number of embodiments of the present invention are described that canbe said to mimic this aspect of human/animal physiology. Also, theanimals use their antagonistic muscle pairs to vary joint stiffness bychanging the static lengths of the muscles that span the joint. Varyingjoint stiffness can help the energetics of locomotion over various typesof terrain and using various gaits.

FIG. 3X is view from the side of an actuator device 871, which includesan electroactive polymer roll 801. Device 871 starts with theconfiguration of device 870. As described with respect to FIG. 3W, thepolymer roll 801 is attached to the end caps of support members 840 and841, which are connected via pinned joint 842. Next, the polymer roll801 is secured to the support member 841 at attachment point 845. Forinstance, the polymer may be pinned to support member 841 at attachmentpoint 845.

Two cuts are made in the polymer roll along cut lines 846. The cuts mayextend from an outer surface of the polymer roll 801 to an inner surfaceof the polymer roll i.e. slice through the roll 801 from the outersurface into the hollow center portion. The cuts may have the effect ofpreventing forces and moments generated in one portion of the polymerroll from propagating to another portion of the polymer roll.

The cuts along lines 846 may also be made on the opposite of the polymerroll 801 (not shown) to divide the polymer roll 801 into four “musclestrands.” Three of the muscle strands 848 a, 848 b, 848 c are shown inthe figure. Each of the muscle strands may include one or more activeareas that may be actuated. The muscle strands may be controlled and maymove independently of one another. The cut lines allow each strand toslide past the other.

A length of each muscle strand may be defined as the distance betweenits attachment points. With this definition, an unactuated length ofmuscle strands 848 a and 848 c is the distance between its attachmentpoints to the ends members 840 and 841 when members 840 and 841 arevertically aligned. When the members 840 and 841 are vertically aligned,an unactuated length of muscle strand 848 b is shorter then musclestrands 848 a and 848 c because it attachment point is located in themiddle of member 841 rather than at its end point.

When actuated, muscle 848 a is allowed to lengthen between its twoattachment points at base 840 and 841. When actuated muscle 848 b isallowed to lengthen between its two attachment points at base 840 andattachment point 845. The attachment point 845 constrains the muscle 848b from lengthening between attachment point 845 and base 841 as a resultof the actuation of muscle 848 b.

The cut lines are shown extending the length of the roll for illustratedpurposes only. In other embodiments, cut lines may be made that aresmaller i.e., that do not extend the length of the roll. Further, cutlines may be made that are along a portion of the length of the roll,around a portion of the circumference or the roll. In general, the cutlines may be made along any 2-D curve on the outer surface of the roll.Further, the cut line may extend through all of the layers of thepolymer roll or through only a portion of the layers of the polymerroll.

In another embodiment (see FIG. 3Z), the polymer roll may be first cutthen secured at the attachment point rather than attached and then cut.Further, the cuts and the resulting muscle strands do not have to bearranged symmetrically about the circumference of the polymer roll.

In operation, device 871 may be actuated in a manner similar to device870. Muscle strand 848 a may be actuated such that it lengthens. Thelengthening of muscle strand 848 a and the initial strain placed onmuscle strands 848 b and 848 c results in moments that rotate member840. As previously described, this can be said to be mimic the workingsof an antagonistic muscle pair in a human body.

After actuation of muscle strand 848 a, muscle strand 848 b may beactuated to more precisely match a desired angle between support members840 and 841. For example, muscle strand 848 a may be actuated so thatthe angle between the support members is smaller than desired. Then,muscle strand 848 b may be actuated to increase the angle and to moreclosely match the desired angle. In general, the changes in angleproduced by muscle strand 848 a may be greater than the changes in anglegenerated by muscle strand 848 b.

As previously describe, this can be said to mimic large and small muscleworking together in the human body where the large muscle control grossmovements and the small muscles control fine movements. A larger musclestrand may be used to generate the same amount of movement as a smallermuscle strand. However, an advantage of using a smaller muscle strand isthat it may require less energy and may afford more precision than usinga larger muscle strand.

In FIG. 3Y, another example of a polymer roll device 872 that uses“muscle strands” is shown. In the figure, support members 850 and 851are connected via a ball and socket joint 852. With the ball and socketjoint 852, the position of member 850 relative to member 851 may bedefined by two angles.

An electroactive polymer roll 801 may be generated, stretched andattached to the ends of support members 850 and 851 as was described fordevices 870 and 871. Then, a number of cuts may be made in the polymerroll 801 and attachment points added to create muscle strands of varyinglengths. The polymer roll may be initially patterned so that activeareas of a desired length are between the attachment points.

In FIG. 3Y, four cut lines 854 are made in the polymer roll and 5attachment points to the support members are used. The cut lines andattachment points are used to create two long muscle strands 855, twoshort muscle strands 853 and one medium muscle strand 856. In operation,the long, medium and short muscle strands may be actuated independentlyto generate gross, medium and fine movements of the support members 850and 851 about the ball and socket joint 852. These movements may becontrolled by a logic device connect to the device 872.

In one embodiment of the present invention, the initial strains on eachmuscle strand may be adjusted relative to one another. As is describedwith respect to FIG. 3Y, an electroactive polymer roll 801 may bestretched and fixed to end points 850 and 851 and a number of cuts inthe polymer roll may be made to generate a number of muscle strands.Then, the muscle strands are attached to the support members 850 and 851to generate muscle strands of different lengths and with differentmoments about the ball and socket joint. To attach the muscle strands tothe support members, an attachment point may be identified on the musclestrand. The location of attachment point on the muscle strand may not beinitially aligned with the attachment point on the support member. Thus,prior to attaching the muscle strand to the support member, the musclestrand may be stretched or shrunk to increase or decrease or the initialstrain on the muscle strand.

The process of adjusting the initial strain on a muscle strand isfurther described with respect to FIG. 3Z. Device 873 includes a supportmembers, 850 (not shown) and 851 attached by a ball and socket joint852. Support member includes two attachment points, 861 a and 861 b. Thedevice 873 is shown in an initial stretched position after theattachment of the polymer roll 801 to the ends of two support members850 and 851 (see FIG. 3Y) and initial cuts have been made to create themuscle strands.

Muscle strand 860 includes strand attachment point 862 where the activearea of the muscle strand is above the attachment point. After theinitial stretching of the polymer roll, strand attachment point 862 isaligned support attachment point 861 b. Thus, the strain on the musclestrand 860 may be fixed at the value after the initial stretching byconnecting strand attachment point 862 to attachment point 861 b.Further, the strain on muscle strand 860 may be decreased from its valueafter the initial stretching by connecting strand attachment point 862to attachment point 861 b. In some embodiments, the pre-strain may bedecreased to zero or a compressive strain may be placed on the musclestrand.

In another embodiment, in device 874, a slot 863 may be used to providea range of attachment points of muscle strand 860 to support member 851.In this embodiment, the initial strain muscle strand 860 may beincreased or decreased depending at what location in the slot thesupport attachment point 861 a is fixed. In another embodiment of thepresent invention, the location of the support attachment point 861 amay be varied during the operation of the device 874. Thus, the lengthof muscle strand 860 and hence its strain at a particular position maybe varied to increase the efficiency the device or vary of stiffness ofthe device 874. In one embodiment, another electroactive polymeractuator may be used to adjust the position of the attachment point 861a.

Although not shown, in other embodiments, the devices 871, 872 and 873may include a plurality of mechanical linkages as described above. Thesemechanical linkages may serve as attachment points for the musclestrands shown in device 871, 872 and 873. Further, the mechanicallinkages may be used to connect two more muscle strands together in somemanner.

In addition, a plurality of roll polymer actuators may be coupledtogether in a massively parallel system. For instance, a number of rollpolymer actuators with angular output may be coupled together to producean actuator capable of generating a snake-like motion. In anotherexample, the actuators may be placed in parallel to allow for a starfishlike motion.

Also, these configurations of angular control can be used for stiffnesscontrol. For example, if in FIG. 3L if 801 a and 801 b are actuatedsimultaneously then there will be increased compliance in that directioncompared to the unactuated state. This angular stiffness control canalso be applied to the connections shown in FIG. 3T to provide angularstiffness control in along multiple axis.

Multifunctionality

Electroactive polymers have many functional uses. In addition toactuation, active areas of the present invention may also be used forgeneration and production of electrical energy, sensing, stiffnesscontrol, or damping control.

FIGS. 1A and 1B may be used to show one manner in which the transducerportion 10 converts mechanical energy to electrical energy. For example,if the transducer portion 10 is mechanically stretched by externalforces to a thinner, larger area shape such as that shown in FIG. 1B,and a relatively small voltage difference (less than that necessary toactuate the film to the configuration in FIG. 1B) is applied betweenelectrodes 14 and 16, the transducer portion 10 will contract in areabetween the electrodes to a shape such as in FIG. 1A when the externalforces are removed. Stretching the transducer refers to deflecting thetransducer from its original resting position—typically to result in alarger net area between the electrodes, e.g. in the plane defined bydirections 18 and 20 between the electrodes. The resting position refersto the position of the transducer portion 10 having no externalelectrical or mechanical input and may comprise any pre-strain in thepolymer. Once the transducer portion 10 is stretched, the relativelysmall voltage difference is provided such that the resultingelectrostatic forces are insufficient to balance the elastic restoringforces of the stretch. The transducer portion 10 therefore contracts,and it becomes thicker and has a smaller planar area in the planedefined by directions 18 and 20 (orthogonal to the thickness betweenelectrodes). When polymer 12 becomes thicker, it separates electrodes 14and 16 and their corresponding unlike charges, thus raising theelectrical energy and voltage of the charge. Further, when electrodes 14and 16 contract to a smaller area, like charges within each electrodecompress, also raising the electrical energy and voltage of the charge.Thus, with different charges on electrodes 14 and 16, contraction from ashape such as that shown in FIG. 1B to one such as that shown in FIG. 1Araises the electrical energy of the charge. That is, mechanicaldeflection is being turned into electrical energy and the transducerportion 10 is acting as a ‘generator’.

When a relatively small voltage difference is applied between electrodes14 and 16, deflection of transducer portion 10 will tend to change thevoltage difference between the electrodes or drive charge to or from theelectrodes, or do both, depending on the electrical state imposed on theelectrodes 14 and 16. As polymer 12 changes in size, the changingelectrical properties and voltage may be detected, dissipated, and/orused. For example, the change in voltage difference between theelectrodes may be used to drive current to or from one of the electrodeswhich is dissipated through a resistor.

Some or all of the charge and energy can be removed when the transducerportion 10 is fully contracted in the plane defined by directions 18 and20. Alternatively, some or all of the charge and energy can be removedduring contraction. If the electric field pressure in the polymerincreases and reaches balance with the mechanical elastic restoringforces and external load during contraction, the contraction will stopbefore full contraction, and no further elastic mechanical energy willbe converted to electrical energy. Removing some of the charge andstored electrical energy reduces the electrical field pressure, therebyallowing contraction to continue. The exact electrical behavior of thetransducer portion 10 when operating in generator mode depends on anyelectrical and mechanical loading as well as the intrinsic properties ofpolymer 12 and electrodes 14 and 16.

In some cases, the transducer portion 10 may be described electricallyas a variable capacitor. The capacitance decreases for the shape changegoing from that shown in FIG. 1B to that shown in FIG. 1A. Typically,the voltage difference between electrodes 14 and 16 will be raised bycontraction. This is normally the case, for example, if additionalcharge is not added or subtracted from electrodes 14 and 16 during thecontraction process. The increase in electrical energy, U, may beillustrated by the formula U=0.5 Q²/C, where Q is the amount of positivecharge on the positive electrode and C is the variable capacitance whichrelates to the intrinsic dielectric properties of polymer 12 and itsgeometry. If Q is fixed and C decreases, then the electrical energy Uincreases. The increase in electrical energy and voltage can berecovered or used in a suitable device or electronic circuit inelectrical communication with electrodes 14 and 16. In addition, thetransducer portion 10 may be mechanically coupled to a mechanical inputthat deflects the polymer and provides mechanical energy.

For a transducer having a substantially constant thickness, onemechanism for differentiating the performance of the transducer, or aportion of the transducer associated with a single active area, as beingan actuator or a generator is in the change in net area orthogonal tothe thickness associated with the polymer deflection. For thesetransducers or active areas, when the deflection causes the net area ofthe transducer/active area to decrease and there is charge on theelectrodes, the transducer/active area is converting from mechanical toelectrical energy and acting as a generator. Conversely, when thedeflection causes the net area of the transducer/active area to increaseand charge is on the electrodes, the transducer/active area isconverting electrical to mechanical energy and acting as an actuator.The change in area in both cases corresponds to a reverse change in filmthickness, i.e. the thickness contracts when the planar area expands,and the thickness expands when the planar area contracts. Both thechange in area and change in thickness determine the amount of energythat is converted between electrical and mechanical. Since the effectsdue to a change in area and corresponding change in thickness arecomplementary, only the change in area will be discussed herein for sakeof brevity. In addition, although deflection of an electroactive polymerwill primarily be discussed as a net increase in area of the polymerwhen the polymer is being used in an actuator to produce mechanicalenergy, it is understood that in some cases (i.e. depending on theloading), the net area may decrease to produce mechanical work. Thus,devices of the present invention may include both actuator and generatormodes, depending on how the polymer is arranged and applied.

Electroactive polymers of the present invention may also be configuredas a sensor. Generally, electroactive polymer sensors of this inventiondetect a “parameter” and/or changes in the parameter. The parameter isusually a physical property of an object such as its temperature,density, strain, deformation, velocity, location, contact, acceleration,vibration, volume, pressure, mass, opacity, concentration, chemicalstate, conductivity, magnetization, dielectric constant, size, etc. Insome cases, the parameter being sensed is associated with a physical“event”. The physical event that is detected may be the attainment of aparticular value or state of a physical or chemical property.

An electroactive polymer sensor is configured such that a portion of theelectroactive polymer deflects in response to the change in a parameterbeing sensed. The electrical energy state and deflection state of thepolymer are related. The change in electrical energy or a change in theelectrical impedance of an active area resulting from the deflection maythen be detected by sensing electronics in electrical communication withthe active area electrodes. This change may comprise a capacitancechange of the polymer, a resistance change of the polymer, and/orresistance change of the electrodes, or a combination thereof.Electronic circuits in electrical communication with electrodes detectthe electrical property change. If a change in capacitance or resistanceof the transducer is being measured for example, one applies electricalenergy to electrodes included in the transducer and observes a change inthe electrical parameters.

In one embodiment, deflection is input into an active area sensor insome manner via one or more coupling mechanisms. In one embodiment, thechanging property or parameter being measured by the sensor correspondsto a changing property of the electroactive polymer, e.g. displacementor size changes in the polymer, and no coupling mechanism is used.Sensing electronics in electrical communication with the electrodesdetect change output by the active area. In some cases, a logic devicein electrical communication with sensing electronics of sensorquantifies the electrical change to provide a digital or other measureof the changing parameter being sensed. For example, the logic devicemay be a single chip computer or microprocessor that processesinformation produced by sensing electronics. Electroactive polymersensors are further described in 10/007,705, which is incorporatedherein by reference for all purposes.

An active area may be configured such that sensing is performedsimultaneously with actuation of the active area. For a monolithictransducer, one active area may be responsible for actuation and anotherfor sensing. Alternatively, the same active area of a polymer may beresponsible for actuation and sensing. In this case, a low amplitude,high frequency AC (sensing) signal may be superimposed on the driving(actuation) signal. For example, a 1000 Hz sensing signal may besuperimposed on a 10 Hz actuation signal. The driving signal will dependon the application, or how fast the actuator is moving, but drivingsignals in the range from less than 0.1 Hz to about 1 million Hz aresuitable for many applications. In one embodiment, the sensing signal isat least about 10 times faster than the motion being measured. Sensingelectronics may then detect and measure the high frequency response ofthe polymer to allow sensor performance that does not interfere withpolymer actuation. Similarly, if impedance changes are detected andmeasured while the electroactive polymer transducer is being used as agenerator, a small, high-frequency AC signal may be superimposed on thelower-frequency generation voltage signal. Filtering techniques may thenseparate the measurement and power signals.

Active areas of the present invention may also be configured to providevariable stiffness and damping functions. In one embodiment, open looptechniques are used to control stiffness and/or damping of a deviceemploying an electroactive polymer transducer; thereby providing simpledesigns that deliver a desired stiffness and/or damping performancewithout sensor feedback. For example, control electronics in electricalcommunication with electrodes of the transducer may supply asubstantially constant charge to the electrodes. Alternately, thecontrol electronics may supply a substantially constant voltage to theelectrodes. Systems employing an electroactive polymer transducer offerseveral techniques for providing stiffness and/or damping control. Anexemplary circuit providing stiffness/damping control is provided below.

While not described in detail, it is important to note that active areasand transducers in all the figures and discussions for the presentinvention may convert between electrical energy and mechanical energybi-directionally (with suitable electronics). Thus, any of the rolledpolymers, active areas, polymer configurations, transducers, and devicesdescribed herein may be a transducer for converting mechanical energy toelectrical energy (generation, variable stiffness or damping, orsensing) and for converting electrical energy to mechanical energy(actuation, variable stiffness or damping, or sensing). Typically, agenerator or sensor active area of the present invention comprises apolymer arranged in a manner that causes a change in electric field inresponse to deflection of a portion of the polymer. The change inelectric field, along with changes in the polymer dimension in thedirection of the field, produces a change in voltage, and hence a changein electrical energy.

Often the transducer is employed within a device that comprises otherstructural and/or functional elements. For example, external mechanicalenergy may be input into the transducer in some manner via one or moremechanical transmission coupling mechanisms. For example, thetransmission mechanism may be designed or configured to receivebiologically-generated mechanical energy and to transfer a portion ofthe biologically-generated mechanical energy to a portion of a polymerwhere the transferred portion of the biologically generated mechanicalenergy results in a deflection in the transducer. Thebiologically-generated mechanical energy may produce an inertial forceor a direct force where a portion of the inertial force or a portion ofthe direct force is received by the transmission mechanism. In oneembodiment, the direct force may be from a foot strike.

Conditioning Electronics

Devices of the present invention may also rely on conditioningelectronics that provide or receive electrical energy from electrodes ofan active area for one of the electroactive polymer functions mentionedabove. Conditioning electronics in electrical communication with one ormore active areas may include functions such as stiffness control,energy dissipation, electrical energy generation, polymer actuation,polymer deflection sensing, control logic, etc.

For actuation, electronic drivers may be connected to the electrodes.The voltage provided to electrodes of an active area will depend uponspecifics of an application. In one embodiment, an active area of thepresent invention is driven electrically by modulating an appliedvoltage about a DC bias voltage. Modulation about a bias voltage allowsfor improved sensitivity and linearity of the transducer to the appliedvoltage. For example, a transducer used in an audio application may bedriven by a signal of up to 200 to 100 volts peak to peak on top of abias voltage ranging from about 750 to 2000 volts DC.

Suitable actuation voltages for electroactive polymers, or portionsthereof, may vary based on the material properties of the electroactivepolymer, such as the dielectric constant, as well as the dimensions ofthe polymer, such as the thickness of the polymer film For example,actuation electric fields used to actuate polymer 12 in FIG. 2A mayrange in magnitude from about 0 V/m to about 440 MV/m. Actuationelectric fields in this range may produce a pressure in the range ofabout 0 Pa to about 10 MPa. In order for the transducer to producegreater forces, the thickness of the polymer layer may be increased.Actuation voltages for a particular polymer may be reduced by increasingthe dielectric constant, decreasing the polymer thickness, anddecreasing the modulus of elasticity, for example.

FIG. 4 illustrates an electrical schematic of an open loop variablestiffness/damping system in accordance with one embodiment of thepresent invention. System 130 comprises an electroactive polymertransducer 132, voltage source 134, control electronics comprisingvariable stiffness/damping circuitry 136 and open loop control 138, andbuffer capacitor 140.

Voltage source 134 provides the voltage used in system 130. In thiscase, voltage source 134 sets the minimum voltage for transducer 132.Adjusting this minimum voltage, together with open loop control 138,adjusts the stiffness provided by transducer 132. Voltage source 134also supplies charge to system 130. Voltage source 134 may include acommercially available voltage supply, such as a low-voltage batterythat supplies a voltage in the range of about 1-15 Volts, and step-upcircuitry that raises the voltage of the battery. In this case, voltagestep-down performed by step-down circuitry in electrical communicationwith the electrodes of transducer 132 may be used to adjust anelectrical output voltage from transducer 132. Alternately, voltagesource 134 may include a variable step-up circuit that can produce avariable high voltage output from the battery. As will be described infurther detail below, voltage source 134 may be used to apply athreshold electric field as described below to operate the polymer in aparticular stiffness regime.

The desired stiffness or damping for system 130 is controlled byvariable stiffness/damping circuitry 136, which sets and changes anelectrical state provided by control electronics in system 130 toprovide the desired stiffness/damping applied by transducer 132. In thiscase, stiffness/damping circuitry 36 inputs a desired voltage to voltagesource 134 and/or inputs a parameter to open loop control 138.Alternately, if step-up circuitry is used to raise the voltage source134, circuitry 136 may input a signal to the step-up circuitry to permitvoltage control.

As transducer 132 deflects, its changing voltage causes charge to movebetween transducer 132 and buffer capacitor 140. Thus, externallyinduced expansion and contraction of transducer 132, e.g., from avibrating mechanical interface, causes charge to flow back and forthbetween transducer 132 and buffer capacitor 140 through open loopcontrol 138. The rate and amount of charge moved to or from transducer132 depends on the properties of buffer capacitor 140, the voltageapplied to transducer 132, any additional electrical components in theelectrical circuit (such as a resistor used as open loop control 138 toprovide damping functionality as current passes therethrough), themechanical configuration of transducer 132, and the forces applied to orby transducer 132. In one embodiment, buffer capacitor 140 has a voltagesubstantially equal to that of transducer 132 for zero displacement oftransducer 132, the voltage of system 130 is set by voltage source 134,and open loop control 138 is a wire; resulting in substantially freeflow of charge between transducer 132 and buffer capacitor 140 fordeflection of transducer 132.

Open loop control 138 provides a passive (no external energy supplied)dynamic response for stiffness applied by transducer 132. Namely, thestiffness provided by transducer 132 may be set by the electricalcomponents included in system 130, such as the control electronics andvoltage source 134, or by a signal from control circuitry 136 actingupon one of the electrical components. Either way, the response oftransducer 132 is passive to the external mechanical deflections imposedon it. In one embodiment, open loop control 138 is a resistor. One canalso set the resistance of the resistor to provide an RC time constantrelative to a time of interest, e.g., a period of oscillation in themechanical system that the transducer is implemented in. In oneembodiment, the resistor has a high resistance such that the RC timeconstant of open loop control 138 and transducer 132 connected in seriesis long compared to a frequency of interest. In this case, thetransducer 132 has a substantially constant charge during the time ofinterest. A resistance that produces an RC time constant for theresistor and the transducer in the range of about 5 to about 30 timesthe period of a frequency of interest may be suitable for someapplications. For applications including cyclic motion, increasing theRC time constant much greater than the mechanical periods of interestallows the amount of charge on electrodes of transducer 132 to remainsubstantially constant during one cycle. In cases where the transduceris used for damping, a resistance that produces an RC time constant forthe resistor and the transducer in the range of about 0.1 to about 4times the period of a frequency of interest may be suitable. As one ofskill in the art will appreciate, resistances used for the resistor mayvary based on application, particularly with respect to the frequency ofinterest and the size (and therefore capacitance C) of the transducer132.

In one embodiment of a suitable electrical state used to controlstiffness and/or damping using open loop techniques, the controlelectronics apply a substantially constant charge to electrodes oftransducer 132, aside from any electrical imperfections or circuitdetails that minimally affect current flow. The substantially constantcharge results in an increased stiffness for the polymer that resistsdeflection of transducer 132. One electrical configuration suitable forachieving substantially constant charge is one that has a high RC timeconstant, as described. When the value of the RC time constant of openloop control 138 and transducer 132 is long compared to the frequency ofinterest, the charge on the electrodes for transducer 132 issubstantially constant. Further description of stiffness and/or dampingcontrol is further described in commonly owned patent application Ser.No. 10/053,511, which is described herein for all purposes.

For generation, mechanical energy may be applied to the polymer oractive area in a manner that allows electrical energy changes to beremoved from electrodes in contact with the polymer. Many methods forapplying mechanical energy and removing an electrical energy change fromthe active area are possible. Rolled devices may be designed thatutilize one or more of these methods to receive an electrical energychange. For generation and sensing, the generation and utilization ofelectrical energy may require conditioning electronics of some type. Forinstance, at the very least, a minimum amount of circuitry is needed toremove electrical energy from the active area. Further, as anotherexample, circuitry of varying degrees of complexity may be used toincrease the efficiency or quantity of electrical generation in aparticular active area or to convert an output voltage to a more usefulvalue.

FIG. 5A is block diagram of one or more active areas 600 on a rolledtransducer that connected to power conditioning electronics 610.Potential functions that may be performed by the power conditioningelectronics 610 include but are not limited to 1) voltage step-upperformed by step-up circuitry 602, which may be used when applying avoltage to active areas 600, 2) charge control performed by the chargecontrol circuitry 604 which may be used to add or to remove charge fromthe active areas 600 at certain times, 3) voltage step-down performed bythe step-down circuitry 608 which may be used to adjust an electricaloutput voltage to a transducer. All of these functions may not berequired in the conditioning electronics 610. For instance, sometransducer devices may not use step-up circuitry 602, other transducerdevices may not use step-down circuitry 608, or some transducer devicesmay not use step-up circuitry and step-down circuitry. Also, some of thecircuit functions may be integrated. For instance, one integratedcircuit may perform the functions of both the step-up circuitry 602 andthe charge control circuitry 608.

FIG. 5B is a circuit schematic of an rolled device 603 employing atransducer 600 for one embodiment of the present invention. As describedabove, transducers of the present invention may behave electrically asvariable capacitors. To understand the operation of the rolledtransducer 603, operational parameters of the rolled transducer 603 attwo times, t₁ and t₂ may be compared. Without wishing to be constrainedby any particular theory, a number of theoretical relationshipsregarding the electrical performance the generator 603 are developed.These relationships are not meant in any manner to limit the manner inwhich the described devices are operated and are provided forillustrative purposes only.

At a first time, t₁, rolled transducer 600 may possess a capacitance,C₁, and the voltage across the transducer 600 may be voltage 601, V_(B).The voltage 601, V_(B), may be provided by the step-up circuitry 602. Ata second time t₂, later than time t₁, the rolled transducer 600 mayposses a capacitance C₂ which is lower than the capacitance C₁.Generally speaking, the higher capacitance C1 occurs when the polymertransducer 600 is stretched in area, and the lower capacitance C2 occurswhen the polymer transducer 600 is contracted or relaxed in area.Without wishing to bound by a particular theory, the change incapacitance of a polymer film with electrodes may be estimated by wellknown formulas relating the capacitance to the film's area, thickness,and dielectric constant.

The decrease in capacitance of the rolled transducer 600 between t₁ andt₂ will increase the voltage across the rolled transducer 600. Theincreased voltage may be used to drive current through diode 616. Thediode 615 may be used to prevent charge from flowing back into thestep-up circuitry at such time. The two diodes, 615 and 616, function ascharge control circuitry 604 for rolled transducer 600 which is part ofthe power conditioning electronics 610 (see FIG. 5A). More complexcharge control circuits may be developed depending on the configurationof the generator 603 and the one or more transducers 600 and are notlimited to the design in FIG. 5B.

A rolled transducer may also be used as an electroactive polymer sensorto measure a change in a parameter of an object being sensed. Typically,the parameter change induces deflection in the transducer, which isconverted to an electrical change output by electrodes attached to thetransducer. Many methods for applying mechanical or electrical energy todeflect the polymer are possible. Typically, the sensing of electricalenergy from a transducer uses electronics of some type. For instance, aminimum amount of circuitry is needed to detect a change in theelectrical state across the electrodes.

FIG. 7 is a schematic of a sensor 350 employing a rolled transducer 351according to one embodiment of the present invention. As shown in FIG.7, sensor 350 comprises rolled transducer 351 and various electronics355 in electrical communication with the electrodes included in thetransducer 351. Electronics 355 are designed or configured to add,remove, and/or detect electrical energy from rolled transducer 351.While many of the elements of electronics 355 are described as discreteunits, it is understood that some of the circuit functions may beintegrated. For instance, one integrated circuit may perform thefunctions of both the logic device 365 and the charge control circuitry357.

In one embodiment, the rolled transducer 351 is prepared for sensing byinitially applying a voltage between its electrodes. In this case, avoltage, V_(I), is provided by the voltage 352. Generally, V_(I) is lessthan the voltage required to actuate rolled transducer 351. In someembodiments, a low-voltage battery may supply voltage, V_(I), in therange of about 1-15 Volts. In any particular embodiment, choice of thevoltage, V_(I) may depend on a number of factors such as the polymerdielectric constant, the size of the polymer, the polymer thickness,environmental noise and electromagnetic interference, compatibility withelectronic circuits that might use or process the sensor information,etc. The initial charge is placed on rolled transducer 351 usingelectronics control sub-circuit 357. The electronics control sub-circuit357 may typically include a logic device such as single chip computer ormicrocontroller to perform voltage and/or charge control functions onrolled transducer 351. The electronics control sub-circuit 357 is thenresponsible for altering the voltage provided by voltage 352 toinitially apply the relatively low voltage on rolled transducer 351.

Sensing electronics 360 are in electrical communication with theelectrodes of rolled transducer 351 and detect the change in electricalenergy or characteristics of rolled transducer 351. In addition todetection, sensing electronics 360 may include circuits configured todetect, measure, process, propagate, and/or record the change inelectrical energy or characteristics of rolled transducer 351.Electroactive polymer transducers of the present invention may behaveelectrically in several ways in response to deflection of theelectroactive polymer transducer. Correspondingly, numerous simpleelectrical measurement circuits and systems may be implemented withinsensing electronics 360 to detect a change in electrical energy ofrolled transducer 351. For example, if rolled transducer 351 operates incapacitance mode, then a simple capacitance bridge may be used to detectchanges in rolled transducer 351 capacitance. In another embodiment, ahigh resistance resistor is disposed in series with rolled transducer351 and the voltage drop across the high resistance resistor is measuredas the rolled transducer 351 deflects. More specifically, changes inrolled transducer 351 voltage induced by deflection of the electroactivepolymer are used to drive current across the high resistance resistor.The polarity of the voltage change across resistor then determines thedirection of current flow and whether the polymer is expanding orcontracting. Resistance sensing techniques may also be used to measurechanges in resistance of the polymer included or changes in resistanceof the electrodes. Some examples of these techniques are described incommonly owned patent application Ser. No. 10/007,705, which waspreviously incorporated by reference.

Fabrication

One advantage of rolled electroactive polymers of the present inventionis simplified manufacture to obtain multilayer electroactive polymerdevices. FIGS. 6A-6D describe the manufacture of a rolled electroactivepolymer device in accordance with one embodiment of the presentinvention. While not described in detail, it is understood thatfabrication techniques described below may be manually implemented,automated, or may comprise a combination of manual and automatedtechniques.

Fabrication according to one embodiment of the present invention employsa frame or fixture to facilitate rolling of an electroactive polymer.FIG. 6B illustrates a rolling fixture 650 useful for facilitating therolling of one or more electroactive polymers. Fixture 650 includeslength 652 and width 654 dimensioned according to the desired unrolledcircumferential length and rolled height, respectively, of anelectroactive polymer to be rolled. Smaller electroactive polymers maybe fashioned using fixture 650 by using a portion of the fixture. Forexample, a rolled electroactive polymer may have an unrolledcircumferential length less than height 652. In many cases, theelectroactive polymer to be rolled is initially smaller than the rollingdimensions of fixture 650 and prestrain is used to increase the size ofthe polymer (see FIG. 6C).

Rolling fixture 650 fixtures an electroactive polymer during rolling,which in this context refers to one or more of: a) dimensioning anelectroactive polymer for subsequent rolling, b) establishing andmaintaining a desired prestrain level including holding theelectroactive polymer and overcoming any elastic restoring forces in thepolymer resulting from prestrain stretching, and c) functional receptionof the rolling mechanism or process. Rolling fixture 650 may include anyfeatures or structures that provide or facilitate one of thesefunctions. For example, to minimize bubbles and other defects betweenpolymer layers during rolling, surface 656 is preferably substantiallysmooth with no surface defects that may introduce bumps or otherinconsistencies in the surface of the polymer during rolling.

For some acrylic electroactive polymers, such as the such as VHB 4910acrylic elastomer mentioned above for example, the acrylic has a highadhesion and may adhere to surface 656, thereby complicating the rollingprocess. Surface 656 allows the polymer to be rolled withoutcomplications. In one embodiment to overcome adhesive complications,surface 656 comprises a Teflon coating. In another embodiment in whichfixture 650 is made from a rigid acrylic or when the electroactivepolymer does not have adhesive properties, a tape or other adhesivecontrol layer may be applied to the surface 656 to achieve a desiredadhesiveness between the polymer and fixture rolling surface. Theadhesive control layer eases peeling off of an adhesive polymer duringrolling. In a specific embodiment, a crystal clear tape such as Scotchbrand Crystal Clear Tape as provided by 3M Company of St. Paul, Minn. isused as an adhesive control layer.

When prestrain is applied to the polymer before rolling, receivingsurface 656 preferably provides sufficient adhesion such that theprestrain is maintained by adhesion between the polymer and surface 656.However, as mentioned above, surface 656 is not so adhesive as torestrict peeling off of the polymer during the rolling process. Thiscreates an adhesion range for the interface between surface 656 and thepolymer that depends on the adhesion properties between theelectroactive polymer and rolling surface 656. Thus, selection of arolling surface 656 or an additional adhesive control layer may be usedto control the interface between surface 656 and the polymer.

Fabrication according to the present invention may also rely on one ormore additional fabrication fixtures or devices. Often, prestrain isapplied to an electroactive polymer. This involves stretching polymermaterial, such as a thin film, from an area initially smaller thanrolling dimensions to an area close to the rolling dimensions; andimplies that the polymer must be held that this larger size duringrolling. FIG. 6C illustrates a stretching fixture 660 useful forstretching an electroactive polymer and maintaining prestrain inaccordance with one embodiment of the present invention. Stretchingfixture 660 includes a substantially flat rigid frame 662 that defines acentral opening or hole 664. A polymer 668 is stretched in bothdirections 667 and 669 and adhered to frame 662 perimetrically aroundhole 664. The adhesion between polymer 668 and frame 662 will depend onelectroactive polymer material and frame 662 material. For example,electroactive polymer 668 may be an acrylic polymer with adhesiveproperties and frame 662 may be a rigid acrylic plate that providessignificant adhesion to an acrylic electroactive polymer with adhesiveproperties. In other cases, securing and adhesive mechanisms such asremovable clamps and two way tape may be applied perimetrically, or inportions, about hole 664 to hold the prestrain polymer 668 to frame 660in a desired state of prestrain.

FIG. 6A illustrates a process flow 640 for fabricating electroactivepolymer device comprising a rolled electroactive polymer in accordancewith one embodiment of the present invention. Methods in accordance withthe present invention may include up to several additional steps notdescribed or illustrated herein order not to obscure the presentinvention.

Process flow 640 begins by receiving an electroactive polymer (641). Thepolymer may be a commercially available product such as a commerciallyavailable acrylic elastomer film. Alternatively, the polymer may be afilm produced by one of casting, dipping, spin coating or spraying. Spincoating typically involves applying a polymer mixture on a rigidsubstrate and spinning to a desired thickness. The polymer mixture mayinclude the polymer, a curing agent and a volatile dispersant orsolvent. The amount of dispersant, the volatility of the dispersant, andthe spin speed may be altered to produce a desired polymer. By way ofexample, polyurethane films may be spin coated in a solution ofpolyurethane and tetrahydrofuran (THF) or cyclohexanone. In the case ofsilicon substrates, the polymer may be spin coated on an aluminizedplastic or a silicon carbide. The aluminum and silicon carbide form asacrificial layer that is subsequently removed by a suitable etchant.Films in the range of one micrometer thick may be produced by spincoating in this manner. Spin coating of polymer films, such as silicone,may be done on a smooth non-sticking plastic substrate, such aspolymethyl methacrylate or teflon. The polymer film may then be releasedby mechanically peeling or with the assistance of alcohol or othersuitable release agent.

In one embodiment, prestrain is applied to the polymer, before rolling,by stretching the polymer in one or more directions (642). As describedabove, the prestrain may be anisotropic or isotropic. In one embodiment,prestrain is applied by stretching the polymer from about 300% to about500% in direction 669 and 50% to about 200% in direction 667 as shown inFIG. 6C. In a specific embodiment, prestrain is applied by stretchingthe polymer 400% in direction 669 and 100% in direction 667. Maintainingprestrain includes temporarily fixing the polymer in some manner. Thismay include use of a stretching fixture, such as fixture 660.

Electrodes are then patterned onto opposing surfaces of theelectroactive polymer (643). Specific techniques used to pattern theelectrodes will depend on the electrode type. For carbon greaseelectrodes, the carbon grease may be manually brushed onto the polymerwithin a brush. A stencil or template may be placed over the polymer tohelp define an electrode area during the brushing process. Carbon fibrilelectrodes may also be sprayed onto the polymer within a region definedby a stencil. In this case, a 0.1% dispersion of BN-type fibrils inethyl acetate may be suitable. Time may also be provided for sprayedelectrodes to dry. From about one hour to about eight hours may besuitable in some cases, depending on the composition and amount ofelectrode applied. In one embodiment, a stencil defines an electrodearea region of about 30 cm to about 35 cm by about 2 cm to about 5 cm.FIG. 6E illustrates a substantially rectangular electrode 673 patternedon the facing side of an electroactive polymer held by stretching frame660 in accordance with one embodiment of the present invention.

Both starting and finishing ends of polymer 668 include a portion 671and 677, respectively, that to do not include electrode material.Portion 677 is not electroded to allow an outermost layer for thefinished rolled device that does not include electrodes and acts as abarrier layer for mechanical protection and electrical isolation. Whenpolymer 668 is rolled about a metal spring, portion 671 is notelectroded to provide electrical isolation between inner layerelectrodes at the metal spring.

Leads may also be disposed in electrical communication with theelectrodes. When contact electrodes are used on both sides of polymer668, a lead is attached to each contact electrode on both sides ofpolymer 668. In a specific embodiment, the lead comprises one or morecopper or gold wires placed between aluminum foil and double sided tape.As shown in FIG. 6E, aluminum foil 672 is disposed along the top edge679 of electrode 673 on the facing side of polymer 668. Aluminum foil672 improves charge communication (charge distribution or collection)between electrode 673 and lead 675. Aluminum foil 672 is disposed alongthe edge of electrode 673, such that when the polymer is rolled, thealuminum foil 672 is proximate to either the top or bottom cylindricalend of the rolled device. A lead and aluminum foil are also disposedalong the bottom edge of an electrode patterned on the opposite side ofpolymer 668. For an acrylic electroactive polymer with adhesiveproperties, the aluminum foil may include a portion that overlaps thetop edge of the electrode and onto the adhesive polymer outside theelectrode. This second portion then adheres to the adhesive polymer viathe adhesive properties of the polymer. Lead 675 is disposed on aluminumfoil 672 and secured to aluminum foil 672 using two sided tape placedover top of both lead 675 and aluminum foil 672. In one embodiment, lead675 is a wire. The two sided tape secures lead 675 in position, and alsoprevents any sharp edges on lead 675 from damaging adjacent polymerlayers after rolling. Off-the-shelf aluminum foil and two sided tapesuch as 3M two sided tape may be suitable for use as aluminum foil 672and two sided tape 675, respectively.

In one embodiment, a multiple layer rolled construction is used (644).In this case, a second layer of electroactive polymer 680 is disposed ontop of the electrode polymer 668 (see FIG. 6F). As mentioned before, thelayers in the multiple layer stack need not be the same material. Othertypes of polymer (electroactive polymer or non-electroactive polymer)may be included in the stack, for example, to vary the stiffness of thestack.

For some acrylic electroactive polymers, adhesive properties of theacrylic polymer hold the layers together. In one embodiment, electrodesare not patterned for the second polymer 680. After rolling, electrode673 on the top surface of polymer 668 acts as an electrode for both thetop side of polymer 668 and the bottom side of polymer 680. Afterrolling, the electrode 681 on the bottom side of polymer 668 contactsthe top side of polymer 680 and acts as an electrode for the top side ofpolymer 680. Thus, after rolling, polymer 680 includes electrodes thatcontact both planar surfaces. Another electroded polymer layer may bedisposed on top of polymer 680, along with another polymer layer havingno electrodes. All four may then be rolled. This even-numbered layerconstruction in which one polymer is electroded and the other is not maybe repeated to produce 6 or 8 layer rolls (or more), as desired.

Rolling a flat sheet introduces a strain gradient across the thicknessof the polymer—the strain is greater (in the tensile direction) towardsthe outer surface of the polymer. If a polymer roll is tightly wound, orthick or numerous layers of polymer are incorporated into the roll, thanthe strain difference may make the dimensions and performance of theinner layers different than the outer layers. Thus, a multilayer stackthat is composed of individual layers will have different amounts ofprestrain in the horizontal direction, which corresponds to thecircumferential direction when rolled. Typically, outer layers in themultilayer stack will have a larger prestrain than inner layers.Differential prestrain between layers may result in differentialperformance between layers.

To achieve more consistent prestrain and performance throughout theroll, differing levels of prestrain may be applied to the multilayerstack before rolling. The differing levels of prestrain compensate forthe strain gradient imposed on outer layers of a multilayer stackimposed by rolling. FIGS. 6G and 6H illustrate differing prestrain in amultilayer stack 690 comprising four layers 691. In FIG. 6G-beforerolling, the lighter shading refers to a greater prestrain. In FIG.6H—after rolling, the substantially constant shading refers to asubstantially constant prestrain among the rolled layers 691.

In FIG. 6G, each layer 691 a-d is disposed onto multilayer stack 690with a different amount of prestrain, depending on its position withinthe stack. The strain gradient between layers 691 in FIG. 6G effectivelycancels out the strain gradient introduced by curving the polymer layerswhen rolled. This situation is illustrated by the curved segment 694illustrated in FIG. 6H. Since each layer 691 in the multilayer stack istypically prestrained separately by stretching it on a frame beforeapplying it to the stack, the prestrain of each layer may be madedifferent by stretching it more or less in one or more directions whenit is put on to the frame.

It may also be possible to introduce a strain gradient by soaking amultilayer stack in a liquid that is absorbed into the stack. The liquidcontacts only one side of the stack and is slowly absorbed by thepolymer in the liquid. The amount of absorption at any point in time,and consequently the amount of strain depends on the distance from theliquid bath. An example of a complimentary polymer and liquid pair isthe 3M VHB acrylic described above and polyol ether. In this case, theliquid relaxes the polymer, thereby effectively reducing prestrain inboth orthogonal directions. The effect of the liquid may also becontrolled to some extent by barrier layers and/or temperature control.For example, the liquid may be absorbed at relatively elevatedtemperatures to speed absorption. When the multilayer stack is returnedto room temperature, the absorption will be relatively fixed by thecooler temperature, e.g. little subsequent diffusion of the liquid willtake place. In another embodiment, barrier layers that prevent orinhibit diffusion may be used to achieve different levels of prestrainin layers 691. For example, with a simple two layer laminate, a polymerbarrier may be disposed between the two electroactive polymer layers andused so that liquid is absorbed only into one electroactive polymerlayer. The barrier polymer may be incorporated as a natural part of anelectrode.

Returning to process flow 640, the polymer is typically rolled aboutsome type of structure (645). In the case of a compressive spring, thepolymer is rolled around the spring while compressed. In one embodiment,spring compression during rolling is accomplished by a bolt that passesthrough the center of the spring and threads into inner threads of endpieces on both ends of the spring. When fabrication and process flow 640is complete, the bolt is removed and the spring and polymer will deflectto an equilibrium position determined by the spring and polymerstiffnesses. Alternatively, the bolt and compression may be maintainedafter fabrication but before usage, e.g., during storage, to minimizeany creep in the polymer. In one embodiment, process flow 640 includestreating the spring surface with PTFE release agent to reduce frictionbetween the spring and the polymer film to be rolled onto the spring.

The polymer layer(s) are then rolled (646). In one embodiment, thisincludes placing the polymer, or polymer stack, onto a rolling fixturesuch as fixture 650 shown in FIG. 6B. FIG. 6D illustrates the stretchingfixture 660 of FIG. 6C disposed over the rolling fixture 650 of FIG. 6B.As shown, the inner opening of hole 664 is larger than the outerperiphery of fixture 650. During rolling, an adhesive or glue may beadded to end pieces—or some other structure involved in the rolling—tohelp secure polymer layers to each other, and to help secure polymerlayers to a rigid object involved in the final construction.

Before rolling, the polymer or polymer stack is cut according to theoutside dimensions of fixture 650. In one embodiment where prestrain isused and the polymer is stretched from its resting state, cutting thepolymer may induce defects at the newly formed edges corresponding tocut. Coupled with stretching forces associated with prestrain, thesedefects may propagate through the stretched polymer. To minimize edgedefect formation and propagation, an edge support layer may be disposedon one or both sides of polymer 680 along the edges to be cut. The edgesupport layer is fixed to the outer periphery of the polymer andprovides mechanical support in these regions. The edge support layer maycomprise a layer of clear tape (such as 3M crystal clear tape), kapton,or polyimide, from about 2 mm to about 5 mm in width, for example.

For an acrylic electroactive polymer with adhesive properties, polymermaterial outside of patterned electrodes may adhere to the surface ofthe rolling fixture 650 and help maintain prestrain in the polymerestablished by stretching fixture 660. When the polymer is rolled abouta compression spring, the compressed spring is placed on either end ofthe polymer on rolling fixture 650 and rolled down the length of thepolymer.

The polymer is then secured in its rolled configuration (647). A pieceof double sided tape may also be attached to the portions of the polymerrolled initially, or finally, or both. In either case, the double sidedtape contributes to holding the rolled polymer and prevents unrolling.Glue or another suitable adhesive may also be used to secure andmaintain the rolled configuration of electroactive polymer. If endpieces are used at either end of the rolled electroactive polymer, anadhesive is disposed such that it contacts an end portion of the polymer(when rolled) and the rigid end piece and holds the end piece to thepolymer. An external covering may also be added to the rolledelectroactive polymer. Multiple layers of a thin insulating polymerrolled or wrapped around the electroactive polymer may provide suitablemechanical electrical protection for the electroactive polymer. Forexample, multiple layers of VHB 9460 may be wrapped around electroactivepolymer. In another embodiment, after the rolling, a rigid ring, metalstrip, or plastic strip is tightly wrapped around the portion of therolled polymer on the end piece. Small holes are drilled (if they arenot already established) through the rigid wrap, the polymer stack, andat least a portion of an end piece. Adhesive is applied into the hole,followed by a nail or screw (for a nail, adhesive is not necessary).

Rolled fabrication techniques of the present invention may also be usedto manufacture multilayer electroactive polymer devices. FIGS. 8A-8Cillustrate the fabrication of a multilayer electroactive polymer device820 using rolling techniques in accordance with one embodiment of thepresent invention. FIG. 8B illustrates the manufactured device 820,which comprises a rigid frame 822 and an electroactive polymer layerstack 824 wound about frame 822 multiple times. Frame 822 issubstantially rectangular in its planar profile and includes fourconnected rigid elements 823 a-d that define a hole 825 within theirplanar center.

FIG. 8A illustrates polymer 924 disposed on a stretch frame 926 beforerolling. Frame 922 is placed at one end of stretch frame 926 and rolledalong the polymer 924 end over end. In one embodiment to facilitate endover end rolling, the corners of frame 922 are rounded. After rolling iscomplete and polymer stack 924 is secured in its rolled configuration,device 920 has a multilayer stack on both the top and bottom sides ofhole 925. One of the polymer stacks may be removed, if desired. Anadhesive or glue may be used to secure polymer 924 between each layer orto secure each layer to frame 922. Frame 922 maintains the prestrain onpolymer 924 originally established using stretch frame 926. As shown inFIG. 8B, polymer stack 924 does not span the entire surface area of hole925. It device 920 were to be used in a diaphragm mode, polymer stack924 and frame 922 may be designed such that polymer stack 924 spans theentire area of hole 925.

Device 920 may be used for linear actuation. FIG. 8C illustrates device920 implemented in a pushrod application (after the bottom multilayerstack has been removed). A housing 930 holds frame 922 and allowsslideable linear movement of a pushrod 932. Pushrod 932 is attached topolymer 924 on its top and bottom surfaces and polymer 924 deflectsnormal to hole 925. A spring 934 biases the bottom side of polymer stack924 and forces it into a curved shape at equilibrium, as shown. Inanother embodiment, a biasing gel or other biasing material is appliedto the bottom surface of polymer stack 924. Biasing Actuation of polymerstack 924 causes pushrod 932 to move to the right. Spring 934 resistsdeflection away from the equilibrium shown; and when actuation voltagesare removed from the polymer, spring 934 pulls pushrod 932 and returnsit to the equilibrium position. FIGS. 8D and 8E illustrate sideperspective views of the pushrod application from FIG. 8C before andafter actuation, respectively.

Applications

Rolled electroactive polymer devices of the present invention havenumerous applications. As the present invention includes electroactivepolymer devices that may be implemented to perform actuation, stiffnesscontrol, damping control, sensing, mechanical output, and/or electricalenergy generation, and implemented with a wide variety of designs, thepresent invention finds use in a broad range of applications. Theseapplications include linear and complex actuators, motors, generators,sensors, robotics, toys, pumps, and fluid flow control. Provided beloware several exemplary applications for some of the transducers anddevices described above. The exemplary applications described herein arenot intended to limit the scope of the present invention. As one skilledin the art will appreciate, transducers of the present invention mayfind use in countless applications requiring conversion betweenelectrical and mechanical energy.

Rolled electroactive polymer devices of the present invention arewell-suited as general linear actuators; and applicable to anyapplications where linear actuators are useful.

One common application of rolled electroactive polymer devices of thepresent invention is for robots. One end of a device may be coupled to arobotic link to provide weight bearing, force, stroke, sensing,compliance and motion control capabilities. In one embodiment, a rolledelectroactive polymer is used in conjunction with a robotic leg.Conventionally, locomotion for a legged robot is achieved using a legstructure that supports the robot weight that allows for actuation andstrain sensor functionality. A relatively sophisticated central controlsystem is required to coordinate the actuation and sensor functions. Anelectroactive polymer device however allows the design to combineactuation, sensing, and elastic (spring dynamics) and viscoelastic(compliance/damping functionality) properties in one leg structure.

Significant savings in weight and component count are an obvious benefitto robot applications; however, there are others. An electromagneticactuator or motor is heavy and becomes energy inefficient at small sizesand low speeds. In contrast, a rolled electroactive polymer is lighter,allows higher energy per weight, and better impedance matching to theenvironment. For sensor functionality, no separate sensor is requiredwith an electroactive polymer device. For stiffness or damping control,no separate spring or damper is required with a suitably electricallycontrolled multifunctional rolled electroactive polymer device. Thus,the rolled electroactive polymer reduces the component count (vs. aconventional robotic leg with conventional technology) at each joint orleg structure, greatly reducing weight and complexity. In a specificembodiment, rolled electroactive polymers are used in a robot comprisingsix legs. For example, each leg may have one degree of freedom anddisposed at a backward angle. Here, the rolled electroactive polymerdevice acts as a linear actuator that changes length of the legstructure with polymer deflection. When a rolled electroactive polymerdevice is actuated, a leg length increases and pushes the robot bodyforward. Actuating each of the six legs in turn may then be used forlegged locomotion of the robot.

Two and three degree of freedom rolled actuators may also be used toprovide serpentine robots. In this case, multiple active areas may bedisposed along the axial direction as well as the circumferentialdirection. For example, the serpentine robot may include a rolledelectroactive polymer with 60 radially aligned active areas in a 15×4array. The latter number (4) refers to the number of circumferentiallydisposed active areas (FIG. 3C) while the former number refers to thenumber of circumferentially disposed active area sets (15). Obviously,other numeric combinations are possible.

The multiple degree of freedom devices may also be used in sensor modeto provide multiple degree of freedom sensing. In one embodiment, rolledelectroactive polymer devices of the present invention are implementedin a virtual reality glove or computer input device that includesmultiple active areas to detect linear strain of portions of the glovein the immediate area of each transducer. Each active area may becoupled to the glove using glue or integrated into the glove material.Such a device is useful for virtual reality applications, microsurgicalapplications, and remote surgical applications for example.

The present invention is also well-suited for use with a roboticgripper. Many grasping strategies rely on accurate positioning andcompliant contact. Since an electroactive polymer is backdrivable at thecompliance of the polymer, grippers that employ multiple degree offreedom electroactive polymer based actuators provide a means forcompliant contact—in addition to accurate positioning. For example, amultiple degree of freedom gripper may be designed using rolledelectroactive polymer devices as described with respect to FIG. 3C. Agripper the may then comprise several of these fingers.

CONCLUSION

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents thatfall within the scope of this invention which have been omitted forbrevity's sake. For example, although the present invention has beendescribed in terms of several specific electrode materials, the presentinvention is not limited to these materials and in some cases mayinclude air as an electrode. In addition, although the present inventionhas been described in terms of circular rolled geometries, the presentinvention is not limited to these geometries and may include rolleddevices with square, rectangular, or oval cross sections and profiles.It is therefore intended that the scope of the invention should bedetermined with reference to the appended claims.

1. A method for fabricating an electroactive polymer device, the methodcomprising: disposing at least two electrodes on an electroactivepolymer; rolling the electroactive polymer about at least one of asupport member, a mechanical linkage, an end cap, a base or combinationsthereof to produce an electroactive polymer roll; and securing theelectroactive polymer roll to maintain its rolled configuration.
 2. Themethod of claim 1 wherein the electroactive polymer is rolled about thesupport member coupled to the mechanical linkage.
 3. The method of claim1 wherein the electroactive polymer is rolled about the end caprotationally coupled to the support member and the support memberrigidly coupled to the base.
 4. The method of claim 1 wherein theelectroactive polymer is secured to at least one of the support member,the mechanical linkage, the end cap, the base or combinations thereof.5. The method of claim 4 wherein the polymer roll is secured using atleast one of adhesive, a fastener, a pin, a cap or combinations thereof.6. The method of claim 1, wherein one or more portions of theelectroactive polymer is secured in tension.
 7. The method of claim 1wherein the mechanical linkage is for allowing a force or momentgenerated in a first portion of the electroactive polymer to becommunicated to a second portion of the electroactive polymer
 8. Themethod of claim 1 wherein the support member is for providing at leastone of a force that strains at least a portion of the electroactivepolymer roll, a force for controlling bending in the electroactivepolymer roll, and combinations thereof.
 9. The method of claim 1 furthercomprising cutting the electroactive polymer roll at one or morelocations to limit a propagation of a force or a moment from a firstportion of the electroactive polymer roll to a second portion of theelectroactive polymer roll.
 10. The method of claim 9 wherein theelectroactive polymer roll is cut into a plurality of muscle strands.11. The method of claim 10 wherein the muscle strands are of varyinglengths.
 12. The method of claim 10 wherein the muscle strands aresecured at three or more points.
 13. The device of claim 10 furthercomprising securing end points of a first muscle strand, stretching orcompressing the first muscle strand about an attachment point betweenthe end points to alter a strain in a portion of the first muscle strandand securing the attachment point.
 14. The method of claim 1 wherein theelectroactive polymer is a dielectric elastomer.